Also submit dependencies from docs folder project

Author: mkurz

.github/workflows/dependency-graph.yml

@@ -22,4 +22,7 @@ jobs:
           fetch-depth: 0
           ref: ${{ inputs.ref }}
       - uses: sbt/setup-sbt@v1
+      - uses: scalacenter/sbt-dependency-submission@v3 # for root project
       - uses: scalacenter/sbt-dependency-submission@v3
+        with:
+          working-directory: ./docs/