PP302: Sets a minimum pytest to at least 6

Apply repo-review rule PP302:

	Must have a minversion=, and must be at least 6
	(first version to support pyproject.toml configuration).

pyproject.toml

@@ -101,6 +101,7 @@ check-hidden = true
 ignore-regex = '\b(UE|path/doesnt/exist)\b'
 
 [tool.pytest.ini_options]
+minversion = "8"
 markers = [
   "all_packages: test install with maximum number of packages",
 ]