site_cache_dir: Use `/var/cache` again instead of `/var/tmp` on UNIX (#239)

diff --git a/src/platformdirs/unix.py b/src/platformdirs/unix.py
index 1d0174f..b1a8993 100644
--- a/src/platformdirs/unix.py
+++ b/src/platformdirs/unix.py
@@ -99,8 +99,8 @@
 
     @property
     def site_cache_dir(self) -> str:
-        """:return: cache directory shared by users, e.g. ``/var/tmp/$appname/$version``"""
-        return self._append_app_name_and_version("/var/tmp")  # noqa: S108
+        """:return: cache directory shared by users, e.g. ``/var/cache/$appname/$version``"""
+        return self._append_app_name_and_version("/var/cache")
 
     @property
     def user_state_dir(self) -> str: