Split tool.stubtest.platforms metadata key (#13746)

Co-authored-by: Avasam <samuel.06@hotmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

stubs/uWSGI/METADATA.toml

@@ -12,4 +12,4 @@ extra_description = """\
 # Run stubtest on MacOS as well, to check that the
 # uWSGI-specific parts of stubtest_third_party.py
 # also work there
-platforms = ["linux", "darwin"]
+ci_platforms = ["linux", "darwin"]