Move the `files` submodule over to `snippets` #425

Job	Run time
pyiron / commit-updated-env	6s
pyiron / build-docs	1m 1s
pyiron / black	8s
pyiron / benchmark-tests	48s
pyiron / build-notebooks	2m 7s
pyiron / pip-check	54s
pyiron / unit-tests (ubuntu-latest, 3.11)	1m 2s
pyiron / unit-tests (ubuntu-latest, 3.10)	53s
pyiron / unit-tests (windows-latest, 3.11)	5m 19s
pyiron / unit-tests (macos-11, 3.11)	2m 25s
pyiron / coveralls-and-codacy / Tests-and-Coverage	1m 10s
	15m 53s

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