Switch back to GitHub xz repo

It should be faster.

app/src/main/cpp/CMakeLists.txt

@@ -20,7 +20,7 @@ option(BUILD_TESTING OFF)
 
 FetchContent_Declare(
         liblzma
-        GIT_REPOSITORY https://git.tukaani.org/xz.git
+        GIT_REPOSITORY https://github.com/tukaani-project/xz.git
         GIT_TAG v5.6.1
         PATCH_COMMAND git apply ${CMAKE_CURRENT_LIST_DIR}/0001-Don-t-build-other-binaries.patch || cd .
 )