Disable building SDL_mixer tests/examples

Fixes Android builds.

Author: smoogipoo

External/build.sh

@@ -181,6 +181,6 @@ run_cmake SDL_image ${OUTPUT_LIB/variant/_image} -DCMAKE_PREFIX_PATH=$CMAKE_PREF
 # -DSDLMIXER_MP3_MPG123=OFF is used because upstream build is broken. Fallback to dr_mp3.
 # See: https://github.com/libsdl-org/SDL_mixer/pull/744#issuecomment-3180682130
 # Fixing using the proposed solution causes more issues.
-run_cmake SDL_mixer ${OUTPUT_LIB/variant/_mixer} -DCMAKE_PREFIX_PATH=$CMAKE_PREFIX_PATH -DSDLMIXER_MP3_MPG123=OFF -DSDLMIXER_DEPS_SHARED=OFF -DSDLMIXER_VENDORED=ON
+run_cmake SDL_mixer ${OUTPUT_LIB/variant/_mixer} -DCMAKE_PREFIX_PATH=$CMAKE_PREFIX_PATH -DSDLMIXER_MP3_MPG123=OFF -DSDLMIXER_DEPS_SHARED=OFF -DSDLMIXER_VENDORED=ON -DSDLMIXER_TESTS=OFF -DSDLMIXER_EXAMPLES=OFF
 
 popd