Make test_sbt work despite the sbt binary version resolution bug

Author: prolativ

.github/workflows/ci.yaml

@@ -337,6 +337,8 @@ jobs:
            github.event_name == 'workflow_dispatch'
            && github.repository == 'lampepfl/dotty'
          )"
+    env:
+      RELEASEBUILD: yes
 
     steps:
       - name: Reset existing repo