Looks the original git repository is working again

Revert "CI: use different git repository for xz"

This reverts commit 3f0e675.

.github/workflows/ccpp.yml

@@ -135,7 +135,7 @@ jobs:
       shell: bash
       if: ${{ !steps.cache-qt.outputs.cache-hit }}
       run: |
-        git clone https://github.com/xz-mirror/xz.git
+        git clone https://git.tukaani.org/xz.git
         sed -i 's/#include "config.h"//' xz/src/common/common_w32res.rc
         sed -i 's/PACKAGE_NAME/"liblzma"/' xz/src/common/common_w32res.rc
         sed -i 's/PACKAGE_URL/"https:\/\/tukaani.org\/xz\/"/' xz/src/common/common_w32res.rc