Make checkboxes less rounded. Fixes #25715

Author: andybalaam

res/css/views/elements/_StyledCheckbox.pcss

@@ -16,7 +16,7 @@ limitations under the License.
 
 .mx_Checkbox {
     $size: $font-16px;
-    $border-radius: 0.4rem;
+    $border-radius: 0.27rem;
 
     display: flex;
     align-items: flex-start;