Rename v4 FontAwesome icons to match v5/v6 name

While FontAwesome provides aliases for all icons, we switch to the new names for consistency. See all changes at:
https://fontawesome.com/docs/web/setup/upgrade/upgrade-from-v4#icons-renamed-since-version-4

app/views/execution_environments/index.html.slim

@@ -2,7 +2,7 @@ h1.d-inline-block = ExecutionEnvironment.model_name.human(count: 2)
 
 - if Runner.management_active?
   = button_to( { action: :sync_all_to_runner_management }, { form_class: 'float-right mb-2', class: 'btn btn-success' })
-    i.fa.fa-upload
+    i.fa-solid.fa-upload
     = t('execution_environments.index.synchronize_all.button')
 
 .table-responsive