Bump coverage from 6.3.3 to 6.4 in /dependencies/default (#354)

Bumps [coverage](https://github.com/nedbat/coveragepy) from 6.3.3 to 6.4.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](coveragepy/coveragepy@6.3.3...6.4)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

dependencies/default/constraints.txt

@@ -1,6 +1,6 @@
 async-generator==1.10
 attrs==21.4.0
-coverage==6.3.3
+coverage==6.4
 flaky==3.7.0
 hypothesis==6.46.7
 idna==3.3