ci: replace cancel step with native concurrency pattern

.github/workflows/ci.yaml

@@ -5,18 +5,13 @@ on: [push, pull_request]
 permissions:
   contents: read
 
-jobs:
-  setup:
-    runs-on: ubuntu-latest
-    steps:
-      - name: Cancel previous
-        uses: styfle/cancel-workflow-action@0.12.1
-        with:
-          access_token: ${{ github.token }}
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.ref != 'refs/heads/main' }}
 
+jobs:
   tests:
-    runs-on: ${{ matrix.platform }}
-    needs: [setup]
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -43,7 +38,6 @@ jobs:
 
   go-lint:
     runs-on: ubuntu-latest
-    needs: [setup]
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-go@v5