cache the build

[github-actions]

groupware/.github/workflows/main.yaml

Lines 55 to 60 in 4bb8f5b

	# TODO: cache the build
	- shell: nix-shell --pure --run "bash -euxo pipefail {0}"
	run: |
	# TODO: cache composer dependencies
	# TODO: check why --ignore-platform-req=ext-redis is needed
	composer install --ignore-platform-req=ext-redis

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This issue was generated by todo-issue based on a TODO comment in 4bb8f5b. It's been assigned to @HellPat because they committed the code.