Fix plugin slug script to use correct PR head SHA

Author: colinmurphy

.github/workflows/plugin-artifact-for-pr.yml

@@ -16,14 +16,13 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
-        with:
-          ref: ${{ github.event.pull_request.head.sha }}
-          fetch-depth: 0
 
       - name: Get changed plugin directory
         id: plugin
         run: |
-          bash .github/scripts/get_plugin_slug.sh ${{ github.event.pull_request.base.sha }} ${{ github.sha }}
+          bash .github/scripts/get_plugin_slug.sh \
+            ${{ github.event.pull_request.base.sha }} \
+            ${{ github.event.pull_request.head.sha }}
 
       - name: Create plugin artifact
         uses: ./.github/actions/create-plugin-artifact