CI: Only check conda for pr into stable or rc

Author: Joseph-Edwards

.github/workflows/pip.yml

@@ -1,5 +1,10 @@
 name: Run tests (pip)
-on: [pull_request, workflow_dispatch]
+on:
+  workflow_dispatch:
+  pull_request:
+    branches:
+      - "stable-*"
+      - "rc-*"
 
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}