inline format!() args up to and including rustc_middle

compiler/rustc_expand/src/expand.rs

@@ -803,7 +803,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             &self.cx.sess.parse_sess,
             sym::proc_macro_hygiene,
             span,
-            format!("custom attributes cannot be applied to {}", kind),
+            format!("custom attributes cannot be applied to {kind}"),
         )
         .emit();
     }
@@ -1707,7 +1707,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                         &UNUSED_ATTRIBUTES,
                         attr.span,
                         self.cx.current_expansion.lint_node_id,
-                        format!("unused attribute `{}`", attr_name),
+                        format!("unused attribute `{attr_name}`"),
                         BuiltinLintDiagnostics::UnusedBuiltinAttribute {
                             attr_name,
                             macro_name: pprust::path_to_string(&call.path),