Improve extension upgrade regression test (addendum to #2364)

[jrgemignani]

Note: This PR was created with AI tools and a human.

This is an addendum to PR #2364 with three improvements.

Makefile:

• Replace awk-based synthetic version (minor+1) with an _upgrade_test suffix (e.g., 1.7.0 -> 1.7.0_upgrade_test). The awk approach produced numeric versions like 1.8.0 that could collide with real future upgrade scripts, and the ::int[] cast in the SQL version lookup fails on non-numeric version strings. The _upgrade_test suffix avoids both issues and is unambiguously synthetic.
• Extend the generated cleanup script to also remove repo-root copies of the synthetic files and to self-delete, preventing stale artifacts from accumulating across repeated test runs.

Regression test (regress/sql/age_upgrade.sql):

• Simplify version lookup to directly select the _upgrade_test version via LIKE '%_upgrade_test' instead of picking the highest non-default version with string_to_array(version, '.')::int[] DESC. The old approach would fail with a cast error on the _upgrade_test suffix and was unnecessarily indirect — the test knows exactly what synthetic version the Makefile installed.

modified: Makefile
modified: regress/expected/age_upgrade.out
modified: regress/sql/age_upgrade.sql

[Copilot]

Pull request overview

This PR refines the extension upgrade regression test infrastructure introduced in #2364 by switching to a clearly synthetic “next” version suffix and updating the regression test’s version selection and cleanup behavior.

Changes:

• Change synthetic “next” extension versioning from minor+1 to a _upgrade_test suffix to avoid collisions with real future versions.
• Update the upgrade regression test to select the synthetic version via pattern matching instead of numeric array casting.
• Extend the generated cleanup script to remove additional synthetic artifacts and self-delete.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
Makefile	Generates _upgrade_test synthetic version and expands cleanup script to remove more artifacts.
regress/sql/age_upgrade.sql	Updates lookup logic for selecting the synthetic upgrade target version.
regress/expected/age_upgrade.out	Adjusts expected output to match the updated version-lookup query.

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