2.6.4: Add Windows ARM64 CI; stop mirroring arm64-windows MSI from sbcl.org

github-actions released this 30 Apr 02:34

4cc53f9

Build sbcl for arm64-windows from source using windows-11-arm runner
instead of mirroring the binary from sbcl.org (which lacks :UCRT).
Also add arm64-windows-binary.msi to *ci-supported* in Lakefile so
the mirror job skips it.

Assets 94