[MM-32622] Remove app.WaitForChannelMembership() (#17048)

* Remove app.WaitForChannelMembership

* Fix tests

* Fix test

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

api4/apitestlib.go

@@ -1055,7 +1055,7 @@ func (th *TestHelper) cleanupTestFile(info *model.FileInfo) error {
 func (th *TestHelper) MakeUserChannelAdmin(user *model.User, channel *model.Channel) {
 	utils.DisableDebugLogForTest()
 
-	if cm, err := th.App.Srv().Store.Channel().GetMember(channel.Id, user.Id); err == nil {
+	if cm, err := th.App.Srv().Store.Channel().GetMember(context.Background(), channel.Id, user.Id); err == nil {
 		cm.SchemeAdmin = true
 		if _, err = th.App.Srv().Store.Channel().UpdateMember(cm); err != nil {
 			utils.EnableDebugLogForTest()