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/vim.h

@@ -156,6 +156,7 @@ enum {
   EXPAND_DIFF_BUFFERS,
   EXPAND_BREAKPOINT,
   EXPAND_SCRIPTNAMES,
+  EXPAND_RUNTIME,
   EXPAND_CHECKHEALTH,
   EXPAND_LUA,
 };