fix(tests): Prevent router_test.exs from running async #5533

Job	Run time
Build application and assets	6m 14s
file_changes	7s
Build Docker image	7m 17s
Linting / TypeScript	38s
Linting / JavaScript	23s
Linting / CSS	32s
Linting / Elixir	3m 27s
Unit tests / JavaScript / Mocha	35s
Unit tests / JavaScript & TypeScript / Jest	2m 22s
Type checks / Elixir	3m 39s
Formatting / Elixir	3m 10s
Formatting / JavaScript & TypeScript	27s
Type checks / TypeScript	30s
Unit tests / Elixir / mix coveralls.html	1m 1s
	30m 22s

Provide feedback