fix: `Igniter.Project.MixProject.update/4` now creates non-existing f… #849

Job	Run time
ash-ci / mix deps.get	15s
ash-ci / audit	31s
ash-ci / mix igniter.upgrade	0s
ash-ci / MIX_ENV=test mix.compile	25s
ash-ci / MIX_ENV=dev mix.compile	26s
ash-ci / mix docs	50s
ash-ci / mix credo --strict	5s
ash-ci / mix ash.codegen --check	0s
ash-ci / mix dialyzer	2m 36s
ash-ci / mix format --check-formatted	22s
ash-ci / mix sobelow	7s
ash-ci / mix spark.cheat_sheets --check	4s
ash-ci / mix spark.formatter --check	6s
ash-ci / mix test	1m 40s
ash-ci / mix deps.unlock --check-unused	19s
ash-ci / Deploy docs to GitHub pages.	7s
ash-ci / NIF ${{ matrix.nif }} - ${{ matrix.job.target }} (${{ matrix.job.os }})	0s
ash-ci / Release	0s
	7m 53s

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