[release/9.0.1xx] Update GivenThatWeWantMSBuildToRespectCustomCulture.cs

[edvilme]

Manual backport of #47549

Fixes failing SupportRespectAlreadyAssignedItemCulture_IsNotSupported_BuildShouldFail test by consolidating back with the core only test theory.
This is causing all PRs in sdk main to fail because of a machine rollout that updated VS to 17.13.x yesterday.

Pull Request Overview

This PR backports a change to resolve failing tests caused by a recent VS update by removing the failing test related to custom culture behavior in MSBuild.

• Removed the failing test: SupportRespectAlreadyAssignedItemCulture_IsNotSupported_BuildShouldFail to align with the consolidated test theory.

Comments suppressed due to low confidence (1)

test/Microsoft.NET.Build.Tests/GivenThatWeWantMSBuildToRespectCustomCulture.cs:29

• The removal of the failing test 'SupportRespectAlreadyAssignedItemCulture_IsNotSupported_BuildShouldFail' might reduce coverage for scenarios where a build is expected to fail. Consider adding a comment explaining that this removal is intentional and that related scenarios are either no longer supported or are covered elsewhere.

[Theory]