test(datetime): remove usage of ion-buttons for custom buttons

Author: brandyscarney

core/src/components/datetime/test/basic/index.html

@@ -136,10 +136,10 @@ <h2>Popover - Custom</h2>
             <ion-popover class="datetime-popover" trigger="open-popover" id="custom-popover">
               <ion-datetime>
                 <span slot="title">My Custom Title</span>
-                <ion-buttons slot="buttons">
+                <div slot="buttons">
                   <ion-button color="danger">Destroy</ion-button>
                   <ion-button color="primary">Confirm</ion-button>
-                </ion-buttons>
+                </div>
               </ion-datetime>
             </ion-popover>
           </div>
@@ -150,10 +150,10 @@ <h2>Modal - Custom</h2>
             <ion-modal trigger="open-modal" id="modal">
               <ion-datetime>
                 <span slot="title">My Custom Title</span>
-                <ion-buttons slot="buttons">
+                <div slot="buttons">
                   <ion-button color="danger">Destroy</ion-button>
                   <ion-button color="primary">Confirm</ion-button>
-                </ion-buttons>
+                </div>
               </ion-datetime>
             </ion-modal>
           </div>