Streamline the NDK version used in Android build and CI

[thunderbiscuit]

When using the ubuntu-latest (ubuntu-20.04), the CI has also migrated to NDK version 25 (see issue here).

We should try to use a more recent version of NDK.

[thunderbiscuit]

Updating to the latest NDK is a long-standing issue with uniffi-rs and Rust in general. Here are some links to keep track of some of the conversation and progress around this:

1. Android NDK 25 [firefox-android: main] mozilla/application-services#5442
2. Update Android NDK to 25 mozilla/application-services#5436
3. 94.3.0 release has a linkage problem in some devices mozilla/application-services#5165
4. note: ld: error: unable to find library -lgcc mozilla/rust-android-gradle#75
5. Support Android ndk versions r23-beta3 and up rust-lang/rust#85806
6. Update CI to use Android NDK r25b rust-lang/rust#102332

[thunderbiscuit]

Currently updating to the latest NDK works only for some builds:

The x86_64 version of bdk-android throws a runtime error when used from an x86_64 machine (but not from an M1).

Native library (android-x86-64/libbdkffi.so) not found in resource path (.)

This is a known issue as per the links above.