since windows allows slash or backslash, allow both instead of MAIN_SEPARATOR (#13996)

# Description

I mean't to do this small change the other day but forgot. We probably
shouldn't be using MAIN_SEPARATOR because **\\*.rs is an illegal glob.
So, update this to just use slash.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->

# Tests + Formatting
<!--
Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->

# After Submitting
<!-- If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
-->

crates/nu-command/src/filesystem/glob.rs

@@ -169,12 +169,14 @@ impl Command for Glob {
             });
         }
 
+        // below we have to check / instead of MAIN_SEPARATOR because glob uses / as separator
+        // using a glob like **\*.rs should fail because it's not a valid glob pattern
         let folder_depth = if let Some(depth) = depth {
             depth
         } else if glob_pattern.contains("**") {
             usize::MAX
-        } else if glob_pattern.contains(std::path::MAIN_SEPARATOR) {
-            glob_pattern.split(std::path::MAIN_SEPARATOR).count() + 1
+        } else if glob_pattern.contains('/') {
+            glob_pattern.split('/').count() + 1
         } else {
             1
         };