chore: remove styfle/cancel-workflow-action usage (testing-library#961)

Author: MichaelDeBoey

.github/workflows/validate.yml

@@ -9,7 +9,12 @@ on:
       - 'beta'
       - 'alpha'
       - '!all-contributors/**'
-  pull_request: {}
+  pull_request:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 jobs:
   main:
     # ignore all-contributors PRs
@@ -20,9 +25,6 @@ jobs:
         react: [16.9.0, ^16, ^17]
     runs-on: ubuntu-latest
     steps:
-      - name: 🛑 Cancel Previous Runs
-        uses: styfle/[email protected]
-
       - name: ⬇️ Checkout repo
         uses: actions/checkout@v2
 
@@ -55,9 +57,6 @@ jobs:
       contains('refs/heads/main,refs/heads/beta,refs/heads/next,refs/heads/alpha', github.ref) &&
       github.event_name == 'push' }}
     steps:
-      - name: 🛑 Cancel Previous Runs
-        uses: styfle/[email protected]
-
       - name: ⬇️ Checkout repo
         uses: actions/checkout@v2