fix the reusable precommit so it runs on the correct commit sha

[MintsInc]

Context

The reusable pre-commit workflows across all client repositories were failing when called from the datadog-api-spec repository due to a cross-repository SHA mismatch issue. The workflows were using github.event.pull_request.base.sha and github.event.pull_request.head.sha which refer to commits in the spec repository, but the workflows check out the client repository. This caused pre-commit to fail because these commit SHAs don't exist in the client repository.

This fix is essential for:

• Cross-repository CI: Enables spec repository to validate generated client code using reusable workflows
• MergeQueue compatibility: Required for the centralized CI management approach
• Semantic correctness: Pre-commit should check files changed in the branch, not arbitrary commit ranges from another repository

Changes

Modified Files

• .github/workflows/reusable-pre-commit.yml: Added merge-base commit range determination

Tests

This will be tested by referencing this version of the workflow in a spec PR.

[MintsInc]

• fix the reusable precommit so it runs on the correct commit sha #2854 👈 (View in Graphite)
• master

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