Compress Linux universal release package

`stockfish-ubuntu-x86-64-universal.tar` goes from 94.8MiB to 67.4MiB (tar.gz)

Note that the CI code is written such that it easy to select other compression
schemes in the future (e.g. tar.xz) by simply changing the `archive_ext`
parameter.

closes https://github.com/official-stockfish/Stockfish/pull/6746

No functional change

.github/ci/universal_matrix.json

@@ -4,7 +4,7 @@
       "name": "Ubuntu 22.04 GCC Universal",
       "os": "ubuntu-22.04",
       "simple_name": "ubuntu",
-      "archive_ext": "tar"
+      "archive_ext": "tar.gz"
     },
     {
       "name": "Windows 2022 Mingw-w64 GCC Universal",