Show diff when linter creates untracked changes (viamrobotics#3464)

Author: penguinland

.github/workflows/test.yml

@@ -63,6 +63,8 @@ jobs:
         GEN_DIFF=$(git status -s)
 
         if [ -n "$GEN_DIFF" ]; then
+            echo '"make build lint" resulted in the following untracked changes:' 1>&2
+            git diff
             echo '"make build lint" resulted in changes not in git' 1>&2
             git status
             exit 1