Fix HAML in admin/broadcast_messages/_form.html.haml

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

app/views/admin/broadcast_messages/_form.html.haml

 .broadcast-message.broadcast-banner-message.gl-alert-warning.js-broadcast-banner-message-preview.gl-mt-3{ style: broadcast_message_style(@broadcast_message), class: ('gl-display-none' unless @broadcast_message.banner? ) }
-  = sprite_icon('bullhorn', css_class:'vertical-align-text-top')
+  = sprite_icon('bullhorn', css_class: 'vertical-align-text-top')
   .js-broadcast-message-preview
     - if @broadcast_message.message.present?
       = render_broadcast_message(@broadcast_message)
@@ -7,7 +7,7 @@
       Your message here
 .d-flex.justify-content-center
   .broadcast-message.broadcast-notification-message.preview.js-broadcast-notification-message-preview.mt-2{ class: ('hidden' unless @broadcast_message.notification? ) }
-    = sprite_icon('bullhorn', css_class:'vertical-align-text-top')
+    = sprite_icon('bullhorn', css_class: 'vertical-align-text-top')
     .js-broadcast-message-preview
       - if @broadcast_message.message.present?
         = render_broadcast_message(@broadcast_message)