Mobile app: Update template to Ionic 7

Author: dpalou

templates/mobile_view_activity_page_latest.mustache

@@ -125,8 +125,8 @@
     </ion-item>
     <%#showgroups%>
         <ion-item>
-            <ion-label>{{ 'plugin.mod_customcert.selectagroup' | translate }}</ion-label>
             <ion-select [(ngModel)]="CONTENT_OTHERDATA.group" name="group" (ionChange)="updateContent({cmid: <% cmid %>, courseid: <% certificate.course %>, group: CONTENT_OTHERDATA.group})" interface="popover">
+                <p slot="label">{{ 'plugin.mod_customcert.selectagroup' | translate }}</p>
                 <%#groups%>
                     <ion-select-option [value]="<% id %>"><% name %></ion-select-option>
                 <%/groups%>