ci: harden cancel.yml permissions (#1408)

Author: sashashura

.github/workflows/cancel.yml

@@ -8,8 +8,14 @@ on:
     branches:
       - master
       - next
+
+permissions: {}
+
 jobs:
   cancel:
+    permissions:
+      actions: write #  to cancel/stop running workflows (styfle/cancel-workflow-action)
+
     name: Cancel Previous Runs
     runs-on: ubuntu-latest
     timeout-minutes: 3