Fix Android build on CI

[uilianries]

This PR not only fixes the current build for Android but also simplifies its use by consuming the NDK only from the official Ubuntu docker image provided by Github Actions.

Still, there is a window for improvement, like, caching PEGTL to reduce the build time, but this is a second step for a future PR.

[uilianries]

Android builds passed: https://github.com/taocpp/json/actions/runs/12534222070?pr=157

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.01%. Comparing base (d5fc49b) to head (2225183).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #157   +/-   ##
=======================================
  Coverage   74.01%   74.01%           
=======================================
  Files         257      257           
  Lines        9191     9191           
  Branches      804      804           
=======================================
  Hits         6803     6803           
  Misses       1785     1785           
  Partials      603      603           

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