add cache for node_modules

[github-actions]

groupware/.github/workflows/main.yaml

Lines 75 to 78 in bc4c292

	# TODO: add cache for node_modules
	- name: Install dependencies
	run: pnpm install --frozen-lockfile --strict-peer-dependencies
	- shell: nix-shell --pure --run "bash -euxo pipefail {0}"

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This issue was generated by todo-issue based on a TODO comment in bc4c292. It's been assigned to @HellPat because they committed the code.