build: sometimes we can't run coverage when sterilizing

Makefile

@@ -24,7 +24,7 @@ clean: ## remove generated byte code, coverage reports, and build artifacts
 	find . -name '*.pyc' -exec rm -f {} +
 	find . -name '*.pyo' -exec rm -f {} +
 	find . -name '*~' -exec rm -f {} +
-	coverage erase
+	-coverage erase
 	rm -fr coverage.json
 	rm -fr build/
 	rm -fr dist/