fix(cmdline): don't redraw 'tabline' in Ex mode (#24123)

Redrawing of 'statusline' and 'winbar' are actually already inhibited by
RedawingDisabled in Ex mode.

In Vim there is a check for `msg_scrolled == 0` (which is false in Ex
mode) since Vim doesn't have msgsep. Add a `!exmode_active` check here
in Nvim instead.

src/nvim/ex_getln.c

@@ -791,7 +791,7 @@ static uint8_t *command_line_enter(int firstc, long count, int indent, bool clea
 
   // Redraw the statusline in case it uses the current mode using the mode()
   // function.
-  if (!cmd_silent) {
+  if (!cmd_silent && !exmode_active) {
     bool found_one = false;
 
     FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {