ci: upgrade to codecov/codecov-action@v4 #217

Job	Run time
unittest (debian:bullseye-slim)	29s
system-testing (debian:unstable-slim)	3m 59s
install (debian:bullseye-slim)	12s
unittest (debian:bookworm-slim)	34s
system-testing (ubuntu:jammy)	3m 49s
yamllint	12s
install (debian:bookworm-slim)	16s
unittest (debian:unstable-slim)	32s
system-testing (ubuntu:mantic)	3m 45s
install (debian:testing-slim)	15s
unittest (ubuntu:jammy)	32s
install (ubuntu:jammy)	20s
unittest (ubuntu:mantic)	29s
install (ubuntu:mantic)	14s
	15m 38s

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