Fix CI: Update Codecov configuration and improve integration test strategy #76

Job	Run time
test (3.8)	27s
integration-test (3.9)	37s
test (3.10)	25s
test (3.11)	20s
integration-test (3.8)	38s
test (3.12)	27s
test (3.9)	21s
integration-test (3.12)	33s
integration-test (3.10)	38s
integration-test (3.11)	32s
integration-test-fork-feedback	-1s
build	17s
	5m 14s

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