Bump sqlfluff from 4.2.0 to 4.2.1 in /src (#4475)

Bumps [sqlfluff](https://github.com/sqlfluff/sqlfluff) from 4.2.0 to 4.2.1.
- [Release notes](https://github.com/sqlfluff/sqlfluff/releases)
- [Changelog](https://github.com/sqlfluff/sqlfluff/blob/main/CHANGELOG.md)
- [Commits](sqlfluff/sqlfluff@4.2.0...4.2.1)

---
updated-dependencies:
- dependency-name: sqlfluff
  dependency-version: 4.2.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Barry Pollard <barrypollard@google.com>

Author: dependabot[bot]

src/requirements.txt

@@ -4,4 +4,4 @@ gunicorn==26.0.0
 pytest==9.0.3
 pytest-watch==4.2.0
 pytest-cov==7.1.0
-sqlfluff==4.2.0
+sqlfluff==4.2.1