fix: flaky task test

[tdejager]

Fix for flaky task test, not using remove_var because of: https://doc.rust-lang.org/std/env/fn.remove_var.html

Even though this function is currently not marked as unsafe, it needs to be because invoking it can cause undefined behaviour. The function will be marked unsafe in a future version of Rust. This is tracked in rust#27970.

This function is safe to call in a single-threaded program.

In multi-threaded programs, you must ensure that are no other threads concurrently writing or reading(!) from the environment through functions other than the ones in this module. You are responsible for figuring out how to achieve this, but we strongly suggest not using set_var or remove_var in multi-threaded programs at all.

[ruben-arts]

Lol good catch!