Add platform normalization for windows-11-arm

[ntkme]

JRuby >=9.4.4.0 supports windows on arm: https://github.com/jruby/jruby/releases/tag/9.4.4.0

GitHub Actions recently added new windows-11-arm runner for OSS: https://github.blog/changelog/2025-04-14-windows-arm64-hosted-runners-now-available-in-public-preview/

Name windows-11-arm is normalized to windows-11-arm64 to align similar to how ubuntu and mac runner's names get normalized.

[ntkme]

Blocked as ruby/jruby-dev-builder#14 (comment)

[eregon]

(wrote it at the same time)
This won't work properly because of no native arm64 JDK available on windows-11-arm, same as ruby/jruby-dev-builder#14 (comment) so let's close/pause this until a native arm64 JDK 21 is added to windows-11-arm.

[ntkme]

I removed the windows-11-arm from the runner matrix, and I think we maybe we can get the platform normalization change in so that we only need to add the runner later.

@eregon What do you think?

[eregon]

OK, that's fine