Revert "Hardcode 'main' as GIT_REF for nightly OpenQA job"

Author: legoktm

.github/workflows/nightlies.yml

@@ -93,5 +93,3 @@ jobs:
   openqa-nightly:
     uses: ./.github/workflows/openqa.yml
     secrets: inherit
-    env:
-      GIT_REF: "main"