gha: move cancelaltion into other workflows (#6771)

.github/workflows/benchmarks.yaml

@@ -2,13 +2,6 @@ name: benchmarks
 on: [pull_request, workflow_dispatch]
 
 jobs:
-  cancel_previous:
-    runs-on: ubuntu-latest
-    steps:
-    - name: Cancel Previous Runs
-      uses: styfle/[email protected]
-      with:
-        access_token: ${{ github.token }}
   bench:
     name: run benchmarks
     runs-on: ${{ matrix.os }}
@@ -17,6 +10,10 @@ jobs:
       matrix:
         os: [ubuntu-18.04]
     steps:
+      - name: Cancel Previous Runs
+        uses: styfle/[email protected]
+        with:
+          access_token: ${{ github.token }}
       - uses: actions/setup-python@v2
         with:
             python-version: 3.7