MNT: (deps): Bump coverage from 7.6.4 to 7.6.6 in /ci

Bumps [coverage](https://github.com/nedbat/coveragepy) from 7.6.4 to 7.6.6.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@7.6.4...7.6.6)

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

Signed-off-by: dependabot[bot] <[email protected]>

ci/test_requirements.txt

@@ -1,4 +1,4 @@
 pytest==8.3.3
 netCDF4==1.7.2
-coverage==7.6.4
+coverage==7.6.6
 vcrpy==6.0.2