Bump coverage from 6.3.2 to 7.6.0 in /requirements

Bumps [coverage](https://github.com/nedbat/coveragepy) from 6.3.2 to 7.6.0.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@6.3.2...7.6.0)

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

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

requirements/tests.txt

@@ -1,4 +1,4 @@
 -r dev.txt
-coverage==6.3.2
+coverage==7.6.0
 requests-mock==1.12.1
 tox<5.0.0