Improve commit SHA retrieval by prioritizing user input when provided

[felickz]

1. Checks for sha input first, If the user explicitly sets sha in the analyze or upload-sarif action, that value is used immediately
2. Falls back to git - If no sha input, runs git rev-parse as before
3. Final fallback to GITHUB_SHA - If git fails, uses the environment variable

Ex testing, if a different repo is cloned into the root of the runner - it is not possible to overload the SHA used to upload the SARIF (it will always use the git rev-parse to get the commit sha from the checkoutPath )

• testing-felickz/codeql-scan-another-repo@ff771fb

Risk assessment

For internal use only. Please select the risk level of this change:

• Low risk: Changes are fully under feature flags, or have been fully tested and validated in pre-production environments and are highly observable, or are documentation or test only.
• High risk: Changes are not fully under feature flags, have limited visibility and/or cannot be tested outside of production.

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.
• Code Quality - The changes impact analyses when analysis-kinds: code-quality.
• CCR - The changes impact analyses for Copilot Code Reviews.
• Third-party analyses - The changes affect the upload-sarif action.

Environments:

• Dotcom - Impacts CodeQL workflows on github.com and/or GitHub Enterprise Cloud with Data Residency.
• GHES - Impacts CodeQL workflows on GitHub Enterprise Server.
• Testing/None - This change does not impact any CodeQL workflows in production.

How did/will you validate this change?

• Test repository - This change will be tested on a test repository before merging.
• Unit tests - I am depending on unit test coverage (i.e. tests in .test.ts files).
• End-to-end tests - I am depending on PR checks (i.e. tests in pr-checks).
• Other - Please provide details.
• None - I am not validating these changes.

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

• Feature flags - All new or changed code paths can be fully disabled with corresponding feature flags.
• Rollback - Change can only be disabled by rolling back the release or releasing a new version with a fix.
• Other - Please provide details.

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. Consider whether this requires this change to be released at a particular time rather than as part of a regular release.
  • Alerts - New or existing monitors will trip if something goes wrong with this change.
• Other - Please provide details.

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

• No special considerations - This change can be merged at any time.
• Special considerations - This change should only be merged once certain preconditions are met. Please provide details of those or link to this PR from an internal issue.

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.