gh-actions: only make wheels for a release or on demand.

Author: mr-c

.github/workflows/wheels.yml

@@ -5,10 +5,6 @@ on:
     types: [published]
   workflow_dispatch: {}
   repository_dispatch: {}
-  pull_request:
-  push:
-    branches:
-      - main
 
 concurrency:
   group: wheels-${{ github.event.pull_request.number || github.ref }}