FIX: copy link not working in non secure context (#25053)

In non secure contexts (HTTP vs HTTPS) which many run in development the
`clipboardCopy` method falls back to and an exec hack.

However, callers expect a promise from this method and the fallback just
returns a boolean.

app/assets/javascripts/discourse/app/lib/utilities.js

@@ -494,7 +494,11 @@ export function clipboardCopy(text) {
   }
 
   // ...Otherwise, use document.execCommand() fallback
-  return clipboardCopyFallback(text);
+  if (clipboardCopyFallback(text)) {
+    return Promise.resolve();
+  } else {
+    return Promise.reject();
+  }
 }
 
 // Use this version of clipboardCopy if you must use an AJAX call