do not allow concurrent runs

.github/workflows/check.yml

@@ -2,6 +2,9 @@ name: "Test template"
 on:
   workflow_dispatch: # allows manual triggering
   push:
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 jobs:
   tests:
     runs-on: ${{ matrix.os }}

.github/workflows/check_macos.yml

@@ -4,6 +4,9 @@ on:
   push:
     branches:
       - 'update_n'
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
 jobs:
   tests:
     runs-on: ${{ matrix.os }}