Add git version check for overlay analysis enablement

[Copilot]

Overlay analysis depends on getFileOidsUnderPath, which uses git ls-files --format option introduced in Git 2.38.0. This adds a version check to ensure overlay analysis is only enabled when the git version is new enough.

Changes

• src/git-utils.ts:
  • Added GIT_MINIMUM_VERSION_FOR_OVERLAY constant ("2.38.0")
  • Added getGitVersionOrThrow() function that throws with detailed error messages
  • Added getGitVersion() function with caching and error logging
  • Added gitVersionAtLeast() function for semver comparison
  • Added logGitVersionTelemetry() function to log git version as telemetry diagnostic
  • Added resetCachedGitVersion() for testing support
• src/config-utils.ts: Added git version check in getOverlayDatabaseMode() that falls back to non-overlay analysis with a warning if git is too old
• src/diagnostics.ts: Added makeTelemetryDiagnostic() helper function for creating telemetry-only diagnostics
• src/init-action.ts:
  • Added call to logGitVersionTelemetry() for git version telemetry
  • Refactored bundle-download-telemetry and zstd-availability diagnostics to use makeTelemetryDiagnostic()
• Tests: Added tests for version parsing (including Windows-style versions like 2.40.0.windows.1), caching behavior, and overlay fallback scenarios

When git version is insufficient, users will see:

Cannot build an overlay database because the installed Git version is older than 2.38.0. Falling back to creating a normal full database instead.

Risk assessment

• Low risk: Changes add a precondition check to existing overlay analysis feature. Falls back gracefully to full database creation.

Which use cases does this change impact?

Workflow types:

• Advanced setup - Impacts users who have custom CodeQL workflows.
• Managed - Impacts users with dynamic workflows (Default Setup, CCR, ...).

Products:

• Code Scanning - The changes impact analyses when analysis-kinds: code-scanning.

Environments:

• Dotcom - Impacts CodeQL workflows on github.com and/or GitHub Enterprise Cloud with Data Residency.
• GHES - Impacts CodeQL workflows on GitHub Enterprise Server.

How did/will you validate this change?

• Unit tests - I am depending on unit test coverage (i.e. tests in .test.ts files).

If something goes wrong after this change is released, what are the mitigation and rollback strategies?

• Rollback - Change can only be disabled by rolling back the release or releasing a new version with a fix.

How will you know if something goes wrong after this change is released?

• Telemetry - I rely on existing telemetry or have made changes to the telemetry.
  • Dashboards - I will watch relevant dashboards for issues after the release.

Are there any special considerations for merging or releasing this change?

• No special considerations - This change can be merged at any time.

Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
• Confirm the readme and docs have been updated if necessary.

Original prompt

Overlay analysis depends on getFileOidsUnderPath, which requires a git version of at least 2.38.0. Update the enablement check for overlay to ensure the git version is new enough

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