Disable flaky tests reported in #6574/#6644 #15360

Job	Run time
check-dependency-rules	8s
check-fail-ci	15s
check-markdown	15s
check-workspace	18s
check-readme	3m 11s
preflight / preflight	44s
preflight / ci-versions	59s
test-rust-features	2m 12s
check-rust-feature-propagation	2m 5s
check-toml-format	1m 0s
check-umbrella	2m 22s
fmt	1m 11s
All quick checks passed	1s
	14m 41s

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