Try to get coveralls working again

pyproject.toml

@@ -78,7 +78,7 @@ test-groups = ["dev"]
 test-command = [
     "python -c 'import mwparserfromhell.parser._tokenizer'",
     "pytest {project}/tests -rxs --cov=mwparserfromhell",
-    "if mkdir -p /output; then mv .coverage /output/.coverage.$(uuidgen); fi"
+    "if [[ $RUNNER_OS == Linux ]]; then mkdir -p /output && mv .coverage /output/.coverage.$(uuidgen); fi"
 ]
 
 [tool.pyright]