chore: checkpoint before Python removal

vendor/proc-macro2/tests/features.rs

@@ -0,0 +1,10 @@
+#![allow(clippy::assertions_on_constants, clippy::ignore_without_reason)]
+
+#[test]
+#[ignore]
+fn make_sure_no_proc_macro() {
+    assert!(
+        !cfg!(feature = "proc-macro"),
+        "still compiled with proc_macro?"
+    );
+}