update to 2.20 branches

Author: pstaabp

.github/workflows/produce_pod.yml

@@ -30,15 +30,15 @@ jobs:
         uses: actions/checkout@v3
         with:
           repository: openwebwork/pg
-          ref: develop
+          ref: PG-2.20
           path: pg
           persist-credentials: false
 
       - name: Checkout WW code
         uses: actions/checkout@v3
         with:
           repository: openwebwork/webwork2
-          ref: develop
+          ref: WeBWorK-2.20
           path: webwork2
           persist-credentials: false