Add GitHub environment variables and checkout source in workflow

Need to actually do this

.github/workflows/main.yaml

@@ -14,6 +14,14 @@ jobs:
       contents: read
 
     steps:
+      - name: Set extra GitHub environment variables
+        id: github-env-vars
+        uses: rlespinasse/github-slug-action@v4
+
+      - name: Checkout source
+        id: checkout-source
+        uses: actions/checkout@v4
+
       - name: Schema Validation
         id: schema-validation
         uses: dsanders11/[email protected]