Auto merge of #120593 - maurer:android-bump, r=Mark-Simulacrum,workingjubilee

Update Android in CI

We are currently using a 10+ year old Android image, and it has caused trouble when working on #120326.

Our current NDK (25) only supports API 19+, so we were already out of spec. This PR:

1. Bumps the API used by the emulator in CI to 21, as per [NDK-26's release notes](https://github.com/android/ndk/wiki/Changelog-r26) deprecating 19 and 20 as targets.
2. Bumps the NDK to 26b

try-job: arm-android

Author: bors