NO MERGE debug CI failure by printing pigeon diff

Author: chrisbobbe

tools/check

@@ -175,6 +175,11 @@ files_check() {
 check_no_changes() {
     local change_description="$1"; shift
 
+    cat >&2 <<EOF
+Changes:
+\`git diff -a -- "$@"\` says:
+  $(git diff -a -- "$@")
+EOF
     if git diff --quiet -- "$@" \
             && no_untracked_files "$@"; then
         return