Change tested branch from master to multisite

Our default branch is multisite so we want to test this. Need to remember to change it back before doing a PR to upstream.

Author: ants

.github/workflows/tests.yaml

@@ -4,7 +4,7 @@ on:
   pull_request:
   push:
     branches:
-    - master
+    - multisite
     - 'REL_[0-9]+_[0-9]+'
 
 env: