chore: checkpoint before Python removal

vendor/thiserror/tests/ui/raw-identifier.rs

@@ -0,0 +1,12 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+#[error("error: {r#fn}")]
+pub struct Error {
+    r#fn: &'static str,
+}
+
+fn main() {
+    let r#fn = "...";
+    let _ = format!("error: {r#fn}");
+}