Remove the "Cancelling Duplicates" workflow

There is now a native way to implement this - the `concurrency` key in
workflows - so use that instead.

This removes another action depending on Node 16
(`potiuk/cancel-workflow-runs`).

.github/workflows/helm.yml

@@ -11,6 +11,10 @@ on:
       - '**/*.md'
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   testing:
     if: |

.github/workflows/main.yml

@@ -10,6 +10,10 @@ on:
       - 'site/**'
       - '**/*.md'
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 env:
   CYPRESS_VERIFY_TIMEOUT: 180000 # https://docs.cypress.io/guides/guides/command-line#cypress-verify
   CVAT_VERSION: "local"