Switch doctests back to native cross-compilation, supported since Rust 1.89

https://blog.rust-lang.org/2025/08/07/Rust-1.89.0/#cross-compiled-doctests

.github/workflows/ci.yml

@@ -96,10 +96,15 @@ jobs:
         run: >
           cargo ndk -t arm64-v8a doc --no-deps
 
-      - name: Tests (host build-testing)
+      - name: Build doctests
+        # All doctests are set to no_run, because they require running in the
+        # context of an Android app.
+        # Only run on stable because cross-compiling doctests is only supported
+        # since Rust 1.89.
+        if: ${{ matrix.rust-version == 'stable' }}
         run: |
-          cargo test -F native-activity -F test
-          cargo test -F game-activity -F test
+          cargo test --doc -F native-activity --target aarch64-linux-android
+          cargo ndk -t arm64-v8a -- test --doc -F game-activity
 
   format:
     runs-on: ubuntu-latest