[ci] Check whitespace on PRs

.github/actions/whitespace/action.yml

@@ -0,0 +1,13 @@
+name: Whitespace
+description: Run Whitespace steps
+
+runs:
+  using: composite
+  steps:
+    - name: Check for bad whitespace changes
+      shell: bash
+      run: |
+        set -e -o pipefail
+
+        # On pull requests, HEAD^1 will always be the merge base
+        git diff --check HEAD^1

.github/workflows/linux.yml

@@ -28,6 +28,9 @@ jobs:
       with:
         fetch-depth: 2
 
+    - name: Check whitespace
+      uses: ./.github/actions/whitespace
+
     - name: Lint the code
       uses: ./.github/actions/lint