Integration Tests: Avoid hidden BootFailedException in CoreConfigurationHttpTests

[AndyButland]

Description

This PR set ModelsBuilder:ModelsMode to Nothing in CoreConfigurationHttpTests to prevent a hidden BootFailedException (InMemoryAuto requires the Umbraco.Cms.DevelopmentMode.Backoffice package) that was being silently swallowed during test execution.

We found this in resolving a visible issue for when upgrading NUnit in #22155 for 18.

When the BootFailedException fires during CoreRuntime.StartAsync(), the runtime catches it internally and sets the runtime level to BootFailed. The BootFailedMiddleware then intercepts all incoming HTTP requests and returns a 404 response. Since a 404 is still a non-null HttpResponseMessage, the assertion passes.

So the tests were "passing" but not really validating what they intended — that Umbraco boots successfully with each configuration. They were just confirming that the boot-failure error page is served.

Testing

The build checks will confirm that the tests in CoreConfigurationHttpTests continue to pass.

[Copilot]

Pull request overview

Adjusts the integration test host configuration to prevent a BootFailedException from being triggered (and potentially swallowed) during CoreConfigurationHttpTests execution by disabling ModelsBuilder for these boot-scenario HTTP tests.

Changes:

• Set Umbraco:CMS:ModelsBuilder:ModelsMode to Nothing in CoreConfigurationHttpTests test host setup.
• Add an explanatory comment linking the setting to the BootFailedException scenario.

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[NguyenThuyLan]

Look good to me!