Fix A11y issues on Team Management tab (#23403)

* Change upload div to a button for focus styling

* Fix team membership button resize on focus

* Remove box shadow from focus styling

lms/djangoapps/teams/static/teams/templates/manage.underscore

@@ -27,7 +27,7 @@
                     "users to teams."
                 ) %>
             </p>
-            <div class="upload-team-csv btn action action-primary">
+            <button class="upload-team-csv btn action action-primary">
                 <input
                     id="upload-team-csv-input"
                     type="file"
@@ -35,7 +35,7 @@
                     class="input-overlay-hack"
                 />
                 <%- gettext("Upload Memberships") %>
-            </div>
+            </button>
             <!-- We need to describe the format of the CSV here (TODO MST-49) -->
             <div class="page-banner" hidden>
                 <div class="alert alert-danger" role="alert">

lms/static/sass/views/_teams.scss

@@ -550,6 +550,10 @@
   .action-primary {
     @extend %btn-primary-blue;
 
+    &:focus {
+      border: inherit;
+      box-shadow: none;
+    }
     display: inline-block;
     text-shadow: none;
   }