Backend issuer form validation broken after MDL-71017

Regression from MDL-71017. Specifically 0152fdbdff52b795ba1c6783d1d4b24308d6e09b.

The errors param is a a reference, but it's wiped straight away:
https://github.com/moodle/moodle/blob/07d40a91ee2e4e87ee4aed4f66d4295efabd0a54/admin/tool/oauth2/classes/form/issuer.php#L246-L247

This shouldn't be happening. This results in the validation checks (e.g. checking that the base URL is HTTPS) being thrown outside the form page as exceptions, which isn't great. This wasn't a problem in 3.10, where the aforementioned check displays as a form validation message under the respective form field.

Replication steps:

1. Go to site admin > Server > OAuth 2 Services
2. Create a new 'custom' issuer (using the "Custom' button below the table)
3. Enter the mandatory fields: name, client id and client secret.
4. Enter 'http://example.com' in the Service base URL field
5. Hit enter
   Expected: You see a form validation error on the form
   Actual: You see an exception message and are taken away from the form