MM-45967: Print diff output in go mod tidy (#21984)

https://mattermost.atlassian.net/browse/MM-45967

```release-note
NONE
```

.circleci/config.yml

@@ -140,7 +140,7 @@ jobs:
           command: |
             cd mattermost-server
             make modules-tidy
-            if [[ -n $(git status --porcelain) ]]; then echo "Please tidy up the Go modules using make modules-tidy"; exit 1; fi
+            if [[ -n $(git status --porcelain) ]]; then echo "Please tidy up the Go modules using make modules-tidy"; git diff; exit 1; fi
   check-store-layers:
     docker:
       - image: cimg/go:1.18