Add permissions that were missed on the first pass (#407)

Co-authored-by: otelbot <[email protected]>

Author: opentelemetrybot

.github/workflows/split_monorepo.yaml

@@ -15,6 +15,8 @@ permissions:
 jobs:
   gitsplit:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write # required for pushing changes
     steps:
       - name: checkout
         run: git clone "$GITHUB_SERVER_URL/$GITHUB_REPOSITORY" "$GITHUB_WORKSPACE" && cd "$GITHUB_WORKSPACE" && git checkout $GITHUB_SHA