Update coverage requirement from <7 to <8

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-3.0b1...7.4.4)

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

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

pyproject.toml

@@ -66,7 +66,7 @@ mosquitto = "pytest_mqtt.mosquitto"
 
 [project.optional-dependencies]
 test = [
-  "coverage<7",
+  "coverage<8",
   "pytest<8",
   "pytest-fixture-order<1",
   "pytest-ordering<1",