Add Arm64EC to the list of architectures to check

[dpaoliello]

The arm64ec-pc-windows-msvc target has been promoted to tier 2, so now that there is a prebuilt standard library available for it add it to the list of architectures to check during CI.

[dpaoliello]

do note that where you added it just runs cargo clippy on it, if you wanted to actually run tests, you'll need to add it to the cross section (edit: nevermind, those are for linux)

GitHub just got ARM64 runner support, so we may want to start running the Windows and Linux ARM64 tests on native hardware instead of using cross.

But, yes, for now just adding this to the list of arches to run clippy.