actions: twister: add a cancel job very early on

Cancel using GH runner for faster execution.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

.github/workflows/twister.yaml

@@ -12,8 +12,17 @@ on:
     - cron: '0 0 * * 6'
 
 jobs:
+  twister-build-cleanup:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cancel Previous Runs
+        uses: styfle/cancel-workflow-action@0.6.0
+        with:
+          access_token: ${{ github.token }}
+
   twister-build-prep:
     runs-on: zephyr_runner
+    needs: twister-build-cleanup
     container:
       image: zephyrprojectrtos/ci:v0.18.4
       options: '--entrypoint /bin/bash'
@@ -28,11 +37,6 @@ jobs:
       TESTS_PER_BUILDER: 700
       COMMIT_RANGE: ${{ github.event.pull_request.base.sha }}..${{ github.event.pull_request.head.sha }}
     steps:
-      - name: Cancel Previous Runs
-        uses: styfle/cancel-workflow-action@0.6.0
-        with:
-          access_token: ${{ github.token }}
-
       - name: checkout
         if: github.event_name == 'pull_request_target'
         uses: actions/checkout@v2