Trigger change event on filename input when file template is applied

Add changelog

Follow event trigger convention

app/assets/javascripts/blob/file_template_mediator.js

@@ -235,7 +235,7 @@ export default class FileTemplateMediator {
   }
 
   setFilename(name) {
-    this.$filenameInput.val(name);
+    this.$filenameInput.val(name).trigger('change');
   }
 
   getSelected() {

changelogs/unreleased/issue-42689-new-file-template.yml

+---
+title: Trigger change event on filename input when file template is applied
+merge_request: 16911
+author: Sebastian Klingler
+type: fixed