ci: auto-commit pre-commit changes on dependabot PRs

[probberechts]

When Dependabot updates dependencies in our pyproject.toml and uv.lock, it does not re-export the associated requirements-dev.txt and requirements-docs.txt files. Consequently, when the CI workflow runs, the uv-export pre-commit hook exits with a failure code, and causes the entire CI pipeline to fail, requiring manual intervention to commit the exported files on every Dependabot PR.

This PR updates .github/workflows/test.yml to automatically intercept and commit these changes on Dependabot PRs:

• Grants the pre-commit job contents: write permissions.
• Utilizes stefanzweifel/git-auto-commit-action to automatically commit and push the updated requirements-*.txt
  files back to the PR branch whenever Dependabot is the actor and the pre-commit check fails.
• Normal workflows triggered by actual users remain unchanged; if they fail the pre-commit check, the CI will still halt as expected to ensure the developer reviews the diff.