Ignore panic_fmt lint in macro-comma-behavior-rpass ui test.

Author: m-ou-se

src/test/ui/macros/macro-comma-behavior-rpass.rs

@@ -57,6 +57,7 @@ fn writeln_1arg() {
 //
 // (Example: Issue #48042)
 #[test]
+#[allow(panic_fmt)]
 fn to_format_or_not_to_format() {
     // ("{}" is the easiest string to test because if this gets
     // sent to format_args!, it'll simply fail to compile.