Fix failing "repository_lockdown" CI job by updating actions/github-script to v7

[T-Gro]

The repository_lockdown CI job was failing because actions/github-script@v6 resolved to a SHA (d7906e4ad0b1822421a7e6a35d5ca353c962f410) that is no longer available on GitHub's CDN, causing a 404 when the runner tried to download the action archive.

Updated all three usages of actions/github-script@v6 to actions/github-script@v7 in .github/workflows/repository_lockdown_check.yml. The v7 release is currently available and maintains the same API surface used by the workflow scripts.

[T-Gro]

LGTM – clean revert of the workaround now that Roslyn handles the diagnostics correctly. The ExceptWith logic is the right way to deduplicate, and the new tests cover the key scenarios well.

Two minor suggestions (non-blocking):

1. Rename the HACK methods: Now that the workaround is gone, the TODO comments explaining the HACK names were removed, but the method names still carry the _HACK_PLEASE_REFER_TO_COMMENT_INSIDE suffix. Consider renaming them back to their original names (e.g. VerifyDiagnosticBetweenMarkers, VerifyErrorBetweenMarkers, VerifyErrorAtMarker) since the hack is no longer needed.

2. Warning not duplicated across passes test: The source let x = 42 at module level doesn't produce any warnings (it's a public binding), so allWarnings is always empty and the assertion trivially passes. Consider using source that actually emits a warning (e.g. open System without using anything from it, or a private unused binding) to make the test meaningful.

[github-actions]

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Change path	Release notes path	Description
vsintegration/src	docs/release-notes/.VisualStudio/18.vNext.md	No current pull request URL (#19812) found, please consider adding it