Fix misspellings and enable misspell on ci (#16285)

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

model/role.go

@@ -278,7 +278,7 @@ func (r *Role) MergeChannelHigherScopedPermissions(higherScopedPermissions *Role
 
 		_, presentOnHigherScope := higherScopedPermissionsMap[cp.Id]
 
-		// For the channel admin role always look to the higher scope to determine if the role has ther permission.
+		// For the channel admin role always look to the higher scope to determine if the role has their permission.
 		// The channel admin is a special case because they're not part of the UI to be "channel moderated", only
 		// channel members and channel guests are.
 		if higherScopedPermissions.RoleID == CHANNEL_ADMIN_ROLE_ID && presentOnHigherScope {