Fix skip android sdk install to use the latest released SDK

[marcprux]

The release of Swift 6.3.1 (https://forums.swift.org/t/announcing-swift-6-3-1/) exposed two bugs in skip android sdk install:

1. We weren't fetching the latest Android SDK by default, but rather the first. This PR fixes it so the highest available version is installed.
2. When installing the host toolchain, we use swiftly, which (unfortunately) interprets "6.3" as "6.3.LATEST_PATCH_VERSION".

The combination of these two issues causes a mismatch between the installed host toolchain (6.3.1) and the Swift SDK for Android (6.3), which leads to errors like:

<unknown>:0: error: module compiled with Swift 6.3 cannot be imported by the Swift 6.3.1 compiler: /Users/runner/Library/org.swift.swiftpm/swift-sdks/swift-6.3-RELEASE_android.artifactbundle/swift-android/swift-resources/usr/lib/swift-x86_64/android/Swift.swiftmodule/x86_64-unknown-linux-android.swiftmodule

This PR should fix both these issues.