vim-patch:9.0.1227: no cmdline completion for :runtime

Problem:    No cmdline completion for :runtime.
Solution:   Add completion for :runtime. (closes vim/vim#11853, closes vim/vim#11447)
            Improve the resulting matches.

a6759381a5

src/nvim/usercmd.c

@@ -89,6 +89,7 @@ static const char *command_complete[] = {
   [EXPAND_SYNTIME] = "syntime",
   [EXPAND_SETTINGS] = "option",
   [EXPAND_PACKADD] = "packadd",
+  [EXPAND_RUNTIME] = "runtime",
   [EXPAND_SHELLCMD] = "shellcmd",
   [EXPAND_SIGN] = "sign",
   [EXPAND_TAGS] = "tag",