fix(tests): Use build/msg/en.js instead of msg/messages.js (#6825)

This change had already been made (by PR #6475 amongst other) to
most of the tests, but there were a couple of stragglers that
still mentioned messages.js.

Fixes #6824.

tests/bootstrap_helper.js

@@ -10,7 +10,7 @@
  * This is loaded, via goog.bootstrap(), after the other top-level
  * Blockly modules.  It simply calls goog.require() for each of them,
  * to force the debug module loader to finish loading them before any
- * non-module scripts (like msg/messages.js) that might have
+ * non-module scripts (like msg/en.js) that might have
  * undeclared dependencies on them.
  */
 

tests/playgrounds/shared_procedures.html

@@ -9,7 +9,7 @@
 <script>
   var BLOCKLY_BOOTSTRAP_OPTIONS = {
     additionalScripts: [
-      'msg/messages.js',
+      'build/msg/en.js',
       'node_modules/@blockly/dev-tools/dist/index.js',
     ],
   }