IBX-11747: Admin 405 responses trigger exception loop in prod mode

[Sztig]

🎫 Issue	IBX-11747

Description:

I'm preventing the loping by only processing the error from the main request

        if (!$event->isMainRequest()) {
            return;
        }

I'm also handling the 405 code as a separate case with its own template

            case 405:
                $content = $this->twig->render('@ibexadesign/ui/error_page/405.html.twig');
                break;

This listener had no test coverage previously so I have added that as well, covered both the fix and the expected behavior outside this specific case.

For QA:

Documentation:

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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