ci(semgrep): Update `.semgrepignore`

[evansims]

Changes

This PR updates the .semgrepignore ignore file for our Semgrep security tooling. It adds the auth0/test and auth0/test_async directories to the ignore list so our tooling stops raising false positives by identifying unit test files as production code.

References

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Testing

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Checklist

• [x] I have read the Auth0 general contribution guidelines
• [x] I have read the Auth0 Code of Conduct
• [x] All existing and new tests complete without errors