Bump external/xamarin-android-tools to include android-{major}.0 fallback

Includes dotnet/android-tools#320 which adds a fallback in
TryGetPlatformDirectoryFromApiLevel: when android-{id} doesn't exist
and id is an integer, it also tries android-{id}.0.

This fixes XA5207 for customers whose SDK Manager installs API 37 to
platforms/android-37.0 instead of platforms/android-37.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jonathanpeppers