ensure nightly builds always produce new packages, expand 'changed-files' lists

[jameslamb]

Contributes to rapidsai/build-planning#218

• uses the new patterns for versioning nightly packages (see builds: add support for computing a date-based version component at build time shared-workflows#603), to ensure they're always uploaded on new builds.

For wheels:

# before
26.10.0a55 

# after
26.10.0a55.post260803200854

And for conda:

# before
26.10.0a55[build=cuda12_260803_9da146ef]

# after
26.10.0a55[build=cuda12_260803200854_9da146ef]

Other changes:

• updates changed-files lists to avoid triggering test jobs in PR CI when only .github/workflows/{build,test}.yaml are changed

Notes for Reviewers

How I tested this

See rapidsai/cugraph-gnn#508

[jameslamb]

/merge