build: delete flutter_avif build cache to free disk space

Make CI happy.

Author: realth000

scripts/build-flutter_avif-android.sh

@@ -36,3 +36,8 @@ echo "building flutter_avif Android libs ... OK!"
 
 ls -R "${AVIF_ANDROID_JNILIBS_DIR}"
 find "${AVIF_ANDROID_JNILIBS_DIR}" -type f -name "*.so" -exec md5sum {} +
+
+# Reduce disk space usage, otherwise GitHub CI fails.
+echo "deleting build cache ..."
+find "${AVIF_ROOT}" -name target -delete
+echo "deleting build cache ... OK!"