build: allow workflow_dispatch on scheduled Actions (#37128)

.github/workflows/stale.yml

@@ -1,5 +1,6 @@
 name: 'Close stale issues'
 on:
+  workflow_dispatch:
   schedule:
     # 1:30am every day
     - cron: '30 1 * * *'

.github/workflows/update_appveyor_image.yml

@@ -2,6 +2,7 @@ name: Update AppVeyor Image
 
 # Run chron daily Mon-Fri
 on:
+  workflow_dispatch:
   schedule:
     - cron: '0 8 * * 1-5' # runs 8:00 every business day (see https://crontab.guru)