Run go vet before golangci (#21580)

golangci has terrible error messages
if the code doesn't compile or there
are some basic errors. Doing a go vet
check is a quick way to eliminate any
head scratching.

```release-note
NONE
```

.circleci/config.yml

@@ -203,6 +203,7 @@ jobs:
       - run:
           command: |
             cd mattermost-server
+            go vet ./...
             make golangci-lint
   # Dedicate job for mattermost-vet to make more clear when the job fails
   check-mattermost-vet: