ci: work around open file limitations for docker build #9

Job	Run time
Calculate list of debian distros and docker image tags	6s
build_and_test_backend / mypy	25s
build_and_test_backend / pylint	32s
build_and_test_backend / test (3.10, ubuntu-latest)	1m 32s
build_and_test_backend / test (3.11, ubuntu-latest)	1m 38s
build_and_test_backend / format	23s
build_and_test_frontend / format	48s
build_and_test_frontend / test	49s
build_and_test_frontend / build-app	4m 53s
build_and_test_frontend / build-web	1m 31s
build_and_test_frontend / lint	55s
Build and publish ready made docker containers	23s
Build .deb packages (debian:bookworm)	4m 2s
Attach assets to release	0s
Deploy demo application	0s
	17m 57s

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