Fix typos in PullRequestMergeForm.vue header comment (#21378)

Signed-off-by: Yarden Shoham <hrsi88@gmail.com>

web_src/js/components/PullRequestMergeForm.vue

@@ -1,7 +1,7 @@
 <template>
   <!--
-  if this component is shown, either the user is admin (can do merge without checks), or they is a writer who has the permission to do merge
+  if this component is shown, either the user is an admin (can do a merge without checks), or they are a writer who has the permission to do a merge
-  if the user is a writer and can't do merge now (canMergeNow==false), then only show the Auto Merge for them
+  if the user is a writer and can't do a merge now (canMergeNow==false), then only show the Auto Merge for them
   How to test the UI manually:
   * Method 1: manually set some variables in pull.tmpl, eg: {{$notAllOverridableChecksOk = true}} {{$canMergeNow = false}}
   * Method 2: make a protected branch, then set state=pending/success :