ci: move upload to Codecov to separate job #293

Job	Run time
unittest (debian:bookworm-slim)	27s
unittest (debian:testing-slim)	23s
install (debian:bookworm-slim)	18s
skip-linters (debian:bookworm-slim)	21s
unittest (debian:unstable-slim)	32s
install (debian:testing-slim)	17s
system-testing (debian:testing-slim)	2m 36s
skip-linters (debian:testing-slim)	24s
unittest (ubuntu:jammy)	27s
install (debian:unstable-slim)	19s
system-testing (debian:unstable-slim)	2m 35s
skip-linters (debian:unstable-slim)	20s
unittest (ubuntu:noble)	26s
install (ubuntu:jammy)	21s
system-testing (ubuntu:jammy)	3m 22s
skip-linters (ubuntu:jammy)	28s
unittest (ubuntu:oracular)	27s
install (ubuntu:noble)	19s
system-testing (ubuntu:noble)	3m 28s
skip-linters (ubuntu:noble)	43s
install (ubuntu:oracular)	20s
system-testing (ubuntu:oracular)	2m 52s
skip-linters (ubuntu:oracular)	26s
yamllint	13s
upload-to-codecov	21s
	22m 45s

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