Update accessibility-alt-text-bot.yml

Update our accessibility-alt-text-bot to get:
- delete alt-text-bot comment when there are no longer errors
- edit existing alt-text-bot comments when the error message changes
- more descriptive alt-text-bot message

.github/workflows/accessibility-alt-text-bot.yml

@@ -5,11 +5,11 @@ on:
   pull_request:
     types: [opened, edited]
   issue_comment:
-    types: [created, edited]
+    types: [created, edited, deleted]
   discussion:
     types: [created, edited]
   discussion_comment:
-    types: [created, edited]
+    types: [created, edited, deleted]
 
 permissions:
   issues: write
@@ -23,4 +23,4 @@ jobs:
     if: ${{ github.event.issue || github.event.pull_request || github.event.discussion }}
     steps:
       - name: Get action 'github/accessibility-alt-text-bot'
-        uses: github/accessibility-alt-text-bot@v1.5.0
+        uses: github/accessibility-alt-text-bot@v1.6.0