[no ci] cancel previous workflow if pr is updated (#774)

Co-authored-by: Viktor <viktorxda@users.noreply.github.com>

.github/workflows/matrix_build.yml

@@ -17,6 +17,10 @@ on:
        - '**.md'
   workflow_dispatch:
 
+concurrency:
+  group: ${{ github.head_ref }}
+  cancel-in-progress: true
+
 env:
   MAX_KERNEL_SIZE: 0x200000
   MAX_ROOTFS_SIZE: 0x500000