fix(std/help): collect windows --help output for gui programs (#16019)

# Description
Adding to #15962, I have realized that there are windows gui programs
like `prismlauncher` or `firefox` that do accept the `--help` flag but
won't output on the terminal unless `collect`ed, so now it collects the
output on windows.

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crates/nu-std/std/help/mod.nu

@@ -762,7 +762,7 @@ def external-commands [
     let target_command = $command | str join " " | str replace "^" ""
     print $"(ansi default_italic)Help pages from external command ($target_command | pretty-cmd):(ansi reset)"
     if $env.NU_HELPER? == "--help" {
-        run-external ($target_command | split row " ") "--help"
+        run-external ($target_command | split row " ") "--help" | if $nu.os-info.name == "windows" { collect } else {}
     } else {
         ^($env.NU_HELPER? | default "man") $target_command
     }