Problem/Motivation
ModulesUninstallForm.php assigns string value to ['attributes']['class'] which can cause complication since in most cases Array is expected.
In our case, hook_link_alter() was used in custom module to target links with specific class values and additional classes were appended to them. As soon as we upgraded to 9.4, an error was thrown on visiting admin/modules which was complaining about [] operator not supported for strings.
Of course we could change our custom code, but I believe, in principal, ['attributes']['class'] should be an array, since class often holds multiple values.
Proposed resolution
We can simply put the value in [].
Remaining tasks
Write tests