Run sponsors check only on issue creation

Since PRs don't get secrets at all, the workflow was failing even for PRs from dependabot.

It's expected that contributors will typically create an issue before submitting a PR, so this should be enough to give awareness to issues reported by sponsors.

.github/workflows/sponsors.yml

@@ -2,8 +2,6 @@
 
 name: sponsors
 on:
-  pull_request:
-    types: [opened]
   issues:
     types: [opened]
 
@@ -22,4 +20,4 @@ jobs:
       - name: 💛 sponsors
         run: ./.github/workflows/sponsors.ps1
         env:
-          GH_TOKEN: ${{ secrets.DEVLOOPED_TOKEN }}
+          GH_TOKEN: ${{ secrets.DEVLOOPED_TOKEN }}