Rename Linux universal release package/binary

Rename Linux universal release package from
`stockfish-ubuntu-x86-64-universal.tar.gz`  to
`stockfish-linux-x86-64-universal.tar.gz` (and similar for the binary), as the
bundled binary should run on any Linux distro with glibc >= 2.35 (which is the
glibc version of the Ubuntu 22.04 build server).

Note that the Linux universal binary is built with static libstdc++ linkage, so
this adds no extra dependency.

This change will hopefully make it less confusing for users, and in line with
how we show it on stockfishchess.org (as Linux).

closes https://github.com/official-stockfish/Stockfish/pull/6760

No functional change

.github/ci/universal_matrix.json

@@ -3,7 +3,7 @@
     {
       "name": "Ubuntu 22.04 GCC Universal",
       "os": "ubuntu-22.04",
-      "simple_name": "ubuntu",
+      "simple_name": "linux",
       "archive_ext": "tar.gz"
     },
     {