allow running the wheels workflow in a PR

Author: masklinn

.github/workflows/release-wheels.yml

@@ -1,7 +1,8 @@
 name: Wheels
 
 on:
-  #pull_request:
+  pull_request:
+    types: [labeled]
   workflow_dispatch:
     inputs:
       release:
@@ -16,6 +17,12 @@ jobs:
   py-wheels-matrix:
     name: "generate build matrix"
     runs-on: ubuntu-latest
+    if: >
+      github.event_name == 'workflow_dispatch' ||
+      (
+          github.event_name == 'pull_request' &&
+          github.event.label.name == 'check-wheels'
+      )
     outputs:
       matrix: ${{ steps.make-matrix.outputs.matrix }}
     steps: