Fix misspellings and enable misspell on ci (#16285)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

api4/channel_test.go

@@ -3627,7 +3627,7 @@ func TestGetChannelModerations(t *testing.T) {
 		}
 	})
 
-	t.Run("Retuns the correct value for manage_members depending on whether the channel is public or private", func(t *testing.T) {
+	t.Run("Returns the correct value for manage_members depending on whether the channel is public or private", func(t *testing.T) {
 		scheme := th.SetupTeamScheme()
 		team.SchemeId = &scheme.Id
 		_, err := th.App.UpdateTeamScheme(team)

api4/job_test.go

@@ -199,7 +199,7 @@ func TestDownloadJob(t *testing.T) {
 	_, resp = th.Client.DownloadJob(job.Id)
 	CheckForbiddenStatus(t, resp)
 
-	// System admin trying to download the results of a non-existant job
+	// System admin trying to download the results of a non-existent job
 	_, resp = th.SystemAdminClient.DownloadJob(job.Id)
 	CheckNotFoundStatus(t, resp)