[Github] Cancel previous in-progress code formatting jobs (llvm#106701)

Author: boomanaiden154

.github/workflows/pr-code-format.yml

@@ -13,6 +13,9 @@ jobs:
   code_formatter:
     runs-on: ubuntu-latest
     timeout-minutes: 30
+    concurrency:
+      group: ${{ github.workflow }}-${{ github.event.pull_request.number }}
+      cancel-in-progress: true
     if: github.repository == 'llvm/llvm-project'
     steps:
       - name: Fetch LLVM sources