Remaining `str::replace` usage flagged by clippy::disallowed_methods in module loader

[iammdzaidalam]

While running cargo make run-ci, clippy reports a disallowed_methods warning for:

core/engine/src/module/loader/mod.rs:65

let specifier = specifier.replace('/', "\\");

Since #4123 migrated similar cases to cow_utils::CowUtils::cow_replace to avoid unnecessary allocations, this looks like a remaining instance.

I’d like to send a small PR replacing this with cow_replace.