Edit tags PHP notice and admin notice

[afercia]

In edit-tag-form.php there's an initial check for an empty $tag_ID, when there's no ID a PHP notice is displayed and an admin notice too.

The admin notice should probably have a red border since it's an error (currently it uses the CSS class updated) and probably shouldn't be dismissible since PHP returns and there's nothing else to display.

To reproduce, just don't pass the tag_ID value in the query string:

[afercia]

Screenshots with the proposed patch applied:

[afercia]

Refreshed patch, trying to prevent a couple of potential PHP notices.

[michaelarestad]

This seems more like warning territory to me. Maybe notice-warning would be a better fit.

[afercia]

Refreshed patch, now using notice-warning:

[afercia]

In 35875:

When editing terms, properly display an admin notice-warning when tag_ID is empty.

Also, avoids two related PHP notices when empty or not set (and thus the global $tag is a WP_Error object).

Fixes: #34515.