Enable the errorAssertions govet check for mattermost-server code (#17346)

* Enable the errorAssertions govet check for mattermost-server code

* Removing unnecesary change

* Fixing some tests

* Fixing tests

* Fixing more after merge

* Fixing new offending entries

* Fixing small vet checks

* Fixing new cases detected by govet

* Fixing remote_cluster_test errors

* Fixing assertion

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

app/session_test.go

@@ -465,13 +465,13 @@ func TestGetRemoteClusterSession(t *testing.T) {
 
 	t.Run("Invalid remote token should return error", func(t *testing.T) {
 		session, err := th.App.GetRemoteClusterSession(model.NewId(), remoteId)
-		require.Error(t, err)
+		require.NotNil(t, err)
 		require.Nil(t, session)
 	})
 
 	t.Run("Invalid remote id should return error", func(t *testing.T) {
 		session, err := th.App.GetRemoteClusterSession(token, model.NewId())
-		require.Error(t, err)
+		require.NotNil(t, err)
 		require.Nil(t, session)
 	})
 }