version: fix shadowing a libssh.h symbol

[vszakats]

/Users/runner/work/curl/curl/lib/version.c: In function 'curl_version_info':
/Users/runner/work/curl/curl/lib/version.c:584:15: error: declaration of 'ssh_buffer' shadows a global declaration [-Werror=shadow]
  584 |   static char ssh_buffer[80];
      |               ^~~~~~~~~~
In file included from /Users/runner/work/curl/curl/lib/vssh/ssh.h:35,
                 from /Users/runner/work/curl/curl/lib/urldata.h:185,
                 from /Users/runner/work/curl/curl/lib/altsvc.c:32,
                 from /Users/runner/work/curl/curl/bld/lib/CMakeFiles/libcurl_shared.dir/Unity/unity_0_c.c:4:
/opt/homebrew/include/libssh/libssh.h:99:35: note: shadowed declaration is here
   99 | typedef struct ssh_buffer_struct* ssh_buffer;
      |                                   ^~~~~~~~~~

Ref: https://github.com/curl/curl/actions/runs/10477958747/job/29020250670#step:9:48

Tested via #14614