fix(navmenu): extend Announcements link access to include Admin role

Author: maakinoh

src/Eurofurence.App.Backoffice/Layout/NavMenu.razor

@@ -14,7 +14,7 @@
         <MudNavLink Href="artistAlleyModeration" Icon="@Icons.Material.Outlined.AddModerator">Artist Alley Moderation
         </MudNavLink>
     </AuthorizeView>
-    <AuthorizeView Roles="AnnouncementManager">
+    <AuthorizeView Roles="Admin,AnnouncementManager">
         <MudNavLink Href="Announcements" Icon="@Icons.Material.Outlined.Announcement">Announcements</MudNavLink>
     </AuthorizeView>
     <MudDivider />