[FLINK-34989][ci] Reduce the number of nightly runs per day

We only want to have master run every day. The release branches should be limited to one run every 3rd day.

.github/workflows/nightly-trigger.yml

@@ -35,13 +35,51 @@ jobs:
           - release-1.18
     runs-on: ubuntu-latest
     steps:
-      - name: Trigger Workflow
+      - name: "Flink Checkout"
+        uses: actions/checkout@v4
+        with:
+          persist-credentials: false
+
+      - name: "Select release branch for nightly run"
+        id: select_release_branch
+        run: |
+          release_branches_ordered_by_version="$(git branch -r | grep upstream | grep 'release-[1-9]\.[0-9]*$' | sort --field-separator '-' --key 2V | grep -o '[^/]*$')"
+          newest_release_branch="$(echo $release_branches_ordered_by_version | tail -1 | head -1)"
+          stable_release_branch="$(echo $release_branches_ordered_by_version | tail -2 | head -1)"
+          
+          day_of_year="$(date +%j)"
+          echo "Day of year: $day_of_year"
+          release_branch = none
+          # each release branch should run every 3rd day to reduce load on the Apache Infra runners
+          if [[ "$(( $day_of_year % 3))" -eq 1 ]]; then
+            release_branch="${newest_release_branch}"
+          else if [[ "$(( $day_of_year % 3))" -eq 2 ]]; then
+            release_branch="${stable_release_branch}"
+          fi
+          
+          echo "$release_branch selected for nightly run"
+          echo "release_branch=${release_branch}" >> ${GITHUB_OUTPUT}
+
+      # master should still run every day
+      - name: Trigger master nightly
+        uses: actions/github-script@v7
+        with:
+          script: |
+            github.rest.actions.createWorkflowDispatch({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              workflow_id: 'nightly.yml',
+              ref: 'master'
+            })
+
+      - name: Trigger release branch nightly
         uses: actions/github-script@v7
+        if: ${{ steps.select_release_branch.release_branch != "none" }}
         with:
           script: |
             github.rest.actions.createWorkflowDispatch({
               owner: context.repo.owner,
               repo: context.repo.repo,
               workflow_id: 'nightly.yml',
-              ref: '${{ matrix.branch }}'
+              ref: '${{ steps.select_release_branch.release_branch }}'
             })