test: ensure `parse_argv/1` can be overridden #776

Job	Run time
ash-ci / mix igniter.upgrade	0s
ash-ci / mix deps.get	41s
ash-ci / audit	46s
ash-ci / MIX_ENV=test mix.compile	25s
ash-ci / MIX_ENV=dev mix.compile	20s
ash-ci / mix docs	32s
ash-ci / mix credo --strict	16s
ash-ci / mix ash.codegen --check	0s
ash-ci / Deploy docs to GitHub pages.	4s
ash-ci / mix format --check-formatted	20s
ash-ci / mix sobelow	3s
ash-ci / mix dialyzer	2m 31s
ash-ci / mix spark.cheat_sheets --check	6s
ash-ci / mix spark.formatter --check	10s
ash-ci / mix test	1m 30s
ash-ci / mix deps.unlock --check-unused	20s
ash-ci / Release	0s
	8m 4s

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