Use is not None for GCSToS3Operator match_glob provision check

[DhanushAnegondi]

match_glob is in GCSToS3Operator.template_fields, so the constructor only ever sees the un-rendered Jinja expression, never the value the DAG author meant. The guard that rejects match_glob on an unsupported google provider tested it for truthiness:

if not self.__is_match_glob_supported and match_glob:

which is what validate-operators-init flags, and why the class is on the exemption list.

The check stays in __init__. It is a provision check, not a value check: it asks whether match_glob was supplied, combined with an environment capability the constructor can already answer for itself. It never inspects the value. Per the false-positives section of #70296 those belong in the constructor and get rewritten in place rather than moved — with render_template_as_native_obj=True a provided field can render to None, so the same check in execute() would report a supplied argument as missing; and raising at construction surfaces a static authoring mistake as a Dag import error rather than once per task instance and per retry.

Since #70505 narrowed the hook to sanction is None / is not None reads, the in-place rewrite passes and the exemption entry still goes.

What this changes

• rewrites the guard to match_glob is not None
• removes GCSToS3Operator from scripts/ci/prek/validate_operators_init_exemptions.txt — the hook fails on stale exemptions, so this has to land in the same commit as the fix
• adds three test cases where nothing previously covered this error at all

Behavioural impact

One cell changes, on google providers older than 10.3.0:

match_glob	before	after
omitted (None)	no raise	no raise
"**/*.csv"	raises	raises
""	no raise	raises

match_glob="" was supplied by the user and truthiness read it as absent. An empty glob is not a valid pattern, and on a provider below 10.3.0 it was never going to be honoured anyway — it would have been passed to a GCSHook.list() call that cannot accept it. This is the stricter direction that 05_pull_requests.rst sanctions for provision checks.

Relationship to #70723

Flagging this up front: #70723 is open against the same entry and reaches the same one-line fix. I worked this independently and only found that PR afterwards, so this is not a deliberate competing implementation — I'm raising it because the two diffs are close enough that a reviewer deserves to know rather than discover it.

Where they differ:

• Following the review on Check GCSToS3Operator match_glob support after template rendering #70723 - @potiuk asking for the narrowing, @shahar1 confirming it matches the precedent one-for-one - this PR now also narrows AirflowException to ValueError and drops the now-stale gcs_to_s3.py::1 entry from generated/known_airflow_exceptions.txt, per the Keep S3DeleteObjectsOperator validation in __init__, narrow to ValueError #70359 precedent. The production change is now equivalent to Check GCSToS3Operator match_glob support after template rendering #70723's.
• This PR covers the omitted-argument case, which Check GCSToS3Operator match_glob support after template rendering #70723 does not. Without it the suite only pins the raising direction, so a regression that made the guard unconditional would still pass.

If maintainers prefer #70723 as the base — which is reasonable, it is older and more complete on the exception-type question — I am happy for this to be closed and will offer the missing test case there instead. I would rather that than have two near-identical PRs consuming review time.

Deliberately not changed

• raise AirflowException — kept as-is, for the reason above.
• The unreachable except ImportError. gcs_to_s3.py already does a module-level from airflow.providers.google.cloud.hooks.gcs import GCSHook, so the except ImportError around the function-level from airflow.providers.google import __version__ in __init__ cannot fire — the module import would have failed first. Real, but a separate concern.
• The flatten_structure / keep_directory_structure warning. Reads two fields that are not template fields, so the rule does not apply and the hook does not flag it.

Verification

Run in a WSL checkout, from providers/amazon:

# baseline, before any change
uv run pytest tests/unit/amazon/aws/transfers/test_gcs_to_s3.py -q
# 30 passed

# the new tests against the UNFIXED source, to prove they discriminate
git checkout HEAD~1 -- providers/amazon/src/airflow/providers/amazon/aws/transfers/gcs_to_s3.py
uv run pytest tests/unit/amazon/aws/transfers/test_gcs_to_s3.py -q
# 2 failed, 31 passed - one failure per behavioural change:
#   [value_supplied]                 AirflowException raised, not ValueError  (exception type)
#   [empty_string_is_still_supplied] DID NOT RAISE ValueError                 (polarity)
git checkout HEAD -- providers/amazon/src/airflow/providers/amazon/aws/transfers/gcs_to_s3.py

# with the fix
uv run pytest tests/unit/amazon/aws/transfers/test_gcs_to_s3.py -q
# 33 passed

prek run --from-ref main
# validate-operators-init, ruff, ruff-format and codespell all pass on the changed files.
# Three unrelated hooks fail in my local environment only (breeze not on PATH, and
# AIRFLOW_HOME pointing at the checkout); no code hook fails.

No newsfragment: providers/amazon has no newsfragments/ directory, and providers/AGENTS.md says never to use them for providers.

related: #70296

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