CI: Install Android NDK 21.4.7075529
CI: Install Android NDK 21.4.7075529

This is the version mandated by Godot's gradle setup anyway so it would get
installed when running gradlew. Now we pre-install the correct version.

(cherry picked from commit 7eaf4d445de93ec314f7467919a59b03321e5464)

ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot,ex/godot