Add CI check for trailing whitespace

.pre-commit-config.yaml

@@ -11,6 +11,8 @@ repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v5.0.0
     hooks:
+      - id: trailing-whitespace
+        exclude: '^classes'
       - id: fix-byte-order-marker
       - id: mixed-line-ending
         args: ['--fix=lf']