Cancel ongoing workflows

.github/workflows/bootstrap.yml

 name: Bootstrap
 
+# See: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency.
+concurrency:
+  group: ${{ github.head_ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
 on:
   push:
     branches:

.github/workflows/linux.yml

 name: Linux
 
+# See: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency.
+concurrency:
+  group: ${{ github.head_ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
 on:
   push:
     branches:
@@ -123,7 +128,7 @@ jobs:
       - uses: actions/checkout@v2
 
       - uses: haskell/actions/setup@v1
-        id: setup-haskell
+        id: setup-haskell-extra
         with:
           ghc-version: ${{ matrix.extra-ghc }}
           cabal-version: latest # default, keeping for visibility

.github/workflows/macos.yml

 name: MacOS
 
+# See: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency.
+concurrency:
+  group: ${{ github.head_ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
 on:
   push:
     branches:
@@ -111,4 +116,3 @@ jobs:
       - name: Validate cli-suite
         if: matrix.cli == true
         run: sh validate.sh -j 2 -w ghc-${{ matrix.ghc }} -v ${{ matrix.flags }} -s cli-suite
-

.github/workflows/quick-jobs.yml

 name: Quick jobs
 
+# See: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency.
+concurrency:
+  group: ${{ github.head_ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
 on:
   push:
     branches:

.github/workflows/users-guide.yml

@@ -2,6 +2,11 @@
 
 name: Users guide
 
+# See: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency.
+concurrency:
+  group: ${{ github.head_ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
 on:
   push:
     branches:

.github/workflows/windows.yml

 name: Windows
 
+# See: https://docs.github.com/en/actions/reference/workflow-syntax-for-github-actions#concurrency.
+concurrency:
+  group: ${{ github.head_ref }}-${{ github.workflow }}
+  cancel-in-progress: true
+
 on:
   push:
     branches: