Advanced text editor misc fixes (#29676)

* removed extra space

* Fixed border of edit box in mobile view

* Fixed test

webapp/channels/src/components/advanced_text_editor/advanced_text_editor.scss

@@ -202,6 +202,7 @@
 }
 
 @media screen and (max-width: 768px) {
+    #post-create {
         .AdvancedTextEditor {
             padding: 0;
 
@@ -226,6 +227,7 @@
                 }
             }
         }
+    }
 
     .sidebar--right .post-create__container {
         form {

webapp/channels/src/components/channel_view/__snapshots__/channel_view.test.tsx.snap

@@ -161,7 +161,7 @@ exports[`components/channel_view Should match snapshot with base props 1`] = `
     channelId="channelId"
   />
   <div
-    className="post-create__container"
+    className="post-create__container AdvancedTextEditor__ctr"
     data-testid="post-create"
     id="post-create"
   >

webapp/channels/src/components/channel_view/channel_view.tsx

@@ -171,7 +171,7 @@ export default class ChannelView extends React.PureComponent<Props, State> {
                 <div
                     id='post-create'
                     data-testid='post-create'
-                    className='post-create__container'
+                    className='post-create__container AdvancedTextEditor__ctr'
                 >
                     <AdvancedCreatePost/>
                 </div>