sbt-dependency-graph: Remove test branch trigger

Following the PR instructions, I’m removing the test branch trigger from
this workflow so it only runs on main.

I didn’t sense-check the dependency output this time, but since it was
working before I assume it still is.

.github/workflows/sbt-dependency-graph.yaml

@@ -3,8 +3,7 @@ on:
   push:
     branches:
       - main
-      - sbt-dependency-graph-bbc9cfe33ad7185b
-  workflow_dispatch: 
+  workflow_dispatch:
 jobs:
   dependency-graph:
     runs-on: ubuntu-latest