Bump to dotnet/android-tools@a428178 (#1400)

Bumps [external/xamarin-android-tools](https://github.com/xamarin/xamarin-android-tools) from `ec5040a` to `a428178`.
- [Commits](dotnet/android-tools@ec5040a...a428178)

---
updated-dependencies:
- dependency-name: external/xamarin-android-tools
  dependency-version: a4281785292065ab7f5c0298f0f88f51b73ffb2c
  dependency-type: direct:production
...

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