Update coverage requirement from ^5.5 to ^6.2

Updates the requirements on [coverage](https://github.com/nedbat/coveragepy) to permit the latest version.
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@coverage-5.5...6.2)

---
updated-dependencies:
- dependency-name: coverage
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <support@github.com>

pyproject.toml

@@ -40,7 +40,7 @@ black = {version = "^21.5-beta.1", python = "^3.7"}
 mkdocs = "^1.2.1"
 mkdocs-material = "^8.1.4"
 mdx-include = "^1.4.1"
-coverage = {extras = ["toml"], version = "^5.5"}
+coverage = {extras = ["toml"], version = "^6.2"}
 autoflake = "^1.4"
 isort = "^5.9.3"