got the condition flipped

ci-tools/update-nixpkgs

@@ -42,7 +42,7 @@ git checkout "${TARGET_BRANCH}" || git checkout -b "${TARGET_BRANCH}"
 nix-shell ./shell.nix --run update-nixpkgs
 
 # Show us what we did
-if ! git diff --exit-code; then
+if git diff --exit-code; then
     echo "No changes."
     exit 0
 fi