update banner command to respect use_ansi_colors (#14684)

# Description

This PR goes along with the recent changes by @cptpiepmatz for
[auto-color](https://github.com/nushell/nushell/pull/14647) and
[evaluation of
auto-color](https://github.com/nushell/nushell/pull/14683) which also
looks at env vars along with config settings to determine when it's
appropriate to show ansi coloring since it's more complicated than just
reading a setting or an env var.


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crates/nu-std/std/core/mod.nu

@@ -30,7 +30,7 @@ It's been this long since (ansi green)Nushell(ansi reset)'s first commit:
 "
 }
 
-match $env.config?.use_ansi_coloring? {
+match (config use-colors) {
     false => { $banner_msg | ansi strip }
     _ => $banner_msg
 }