`RuntimeInformation.ProcessArchitecture` returns X64 architecture for Arm64 tests

.NET version

7.0

Did it work in .NET Framework?

No

Did it work in any of the earlier releases of .NET Core or .NET 5+?

No response

Issue description

Tests are run for x86, x64 and arm64 architectures. Some tests could be flaky on a specific architecture, so we introduced an attribute to skip a test when run on a certain architecture (https://github.com/dotnet/winforms/pull/6599). The attribute uses the System.Runtime.InteropServices.RuntimeInformation.ProcessArchitecture property to determine the architecture. However, this property returns Architecture.X64 for arm64 tests, which makes skipping tests for arm64 not working as expected.

For example, while DataGridViewTests.DataGridView_ColumnHeadersHeight_SetWithHandle_GetReturnsExpected has following attribute:

[ConditionalWinFormsTheory(UnsupportedArchitecture = Architecture.Arm64,
    Skip = "Flaky tests, see: https://github.com/dotnet/winforms/issues/6597")]

it is still executed on arm64:

Steps to reproduce

1. Add Arm64 as an unsupported architecture on a unit test.
2. Search for the test in CI pipeline test results.

[RussKie]

Tests on ARM64 are run under x64.

[JeremyKuhne]

@RussKie, @dreddy-work if tests on the ARM leg are run on x64, what is the value? How are they any different than the x64 leg?