ci-lint: check whitespace issues

Was testing this script for a couple weeks on Linux, found no issues, seems reliable. Also tested it on Windows today.

.github/workflows/ci-lint.yaml

@@ -103,6 +103,11 @@ jobs:
           exit $ERROR
         continue-on-error: true
 
+      - name: Check whitespace
+        id: check-whitespace
+        run: poe check-whitespace
+        continue-on-error: true
+
       - name: Final check
         run: |
           ERROR=0
@@ -121,4 +126,7 @@ jobs:
           if [ "${{ steps.ty-ios.outcome }}" != "success" ]; then
             echo "::error::ty check (ios) failed, see 'ty check (ios)' step for the details." && ERROR=1
           fi
+          if [ "${{ steps.check-whitespace.outcome }}" != "success" ]; then
+            echo "::error::Whitespace check failed, see 'Check whitespace' step for the details." && ERROR=1
+          fi
           exit $ERROR