Rollup merge of rust-lang#78898 - SNCPlay42:issue-78892, r=Mark-Simulacrum

add regression test for rust-lang#78892

closes rust-lang#78892, which was already fixed on nightly.

Author: jonas-schievink

src/test/ui/macros/issue-78892-substitution-in-statement-attr.rs

@@ -0,0 +1,14 @@
+// check-pass
+
+// regression test for #78892
+
+macro_rules! mac {
+    ($lint_name:ident) => {{
+        #[allow($lint_name)]
+        let _ = ();
+    }};
+}
+
+fn main() {
+    mac!(dead_code)
+}