ci: move upload to Codecov to separate job #292

Job	Run time
skip-linters (debian:bookworm-slim)	25s
skip-linters (debian:testing-slim)	22s
skip-linters (debian:unstable-slim)	28s
system-testing (debian:testing-slim)	2m 29s
install (debian:bookworm-slim)	20s
skip-linters (ubuntu:jammy)	30s
system-testing (debian:unstable-slim)	2m 45s
unittest (debian:bookworm-slim)	28s
install (debian:testing-slim)	20s
skip-linters (ubuntu:noble)	27s
system-testing (ubuntu:jammy)	3m 22s
install (debian:unstable-slim)	20s
unittest (debian:testing-slim)	28s
skip-linters (ubuntu:oracular)	24s
install (ubuntu:jammy)	30s
system-testing (ubuntu:noble)	3m 26s
unittest (debian:unstable-slim)	27s
unittest (ubuntu:jammy)	35s
install (ubuntu:noble)	21s
system-testing (ubuntu:oracular)	2m 45s
unittest (ubuntu:noble)	26s
install (ubuntu:oracular)	17s
yamllint	12s
unittest (ubuntu:oracular)	24s
upload-to-codecov	19s
	22m 50s

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