Set override locale in toolkit (#8957)

# Description

Very simple change that sets the override locale that's used by
formatting tests

# User-Facing Changes

None

# Tests + Formatting

N/A

# After Submitting

N/A

Co-authored-by: Jelle Besseling <jelle@bigbridge.nl>

toolkit.nu

@@ -199,6 +199,7 @@ def report [
 export def "check pr" [
     --fast: bool  # use the "nextext" `cargo` subcommand to speed up the tests (see [`cargo-nextest`](https://nexte.st/) and [`nextest-rs/nextest`](https://github.com/nextest-rs/nextest))
 ] {
+    let-env NU_TEST_LOCALE_OVERRIDE = 'en_US.utf8';
     try {
         fmt --check --verbose
     } catch {