health.vim: show TUI-related env vars (#7498)

ref #7473
ref #7490

runtime/autoload/health/nvim.vim

@@ -173,6 +173,11 @@ function! s:check_terminal() abort
     call health#report_info('key_dc (kdch1) terminfo entry: '
         \ .(empty(kbs_entry) ? '? (not found)' : kdch1_entry))
   endif
+  for env_var in ['XTERM_VERSION', 'VTE_VERSION', 'TERM_PROGRAM', 'COLORTERM', 'SSH_TTY']
+    if !empty(eval('$'.env_var))
+      call health#report_info(printf("$%s='%s'", env_var, eval('$'.env_var)))
+    endif
+  endfor
 endfunction
 
 function! health#nvim#check() abort