ci: no coverage necessary for hygiene tests

src/test_hygiene/mod.rs

@@ -1,3 +1,10 @@
+// The modules in this test are used to check PyO3 macro expansion is hygienic. By locating the test
+// inside the crate the global `::pyo3` namespace is not available, so in combination with
+// #[pyo3(crate = "crate")] this validates that all macro expansion respects the setting.
+//
+// The generated code is never executed (these tests are checking compile time correctness.)
+#![cfg_attr(coverage, feature(no_coverage))]
+
 mod misc;
 mod pyclass;
 mod pyfunction;