Improve stability of tests in PolyhedralGeometry #16968

Job	Run time
doctest (1.10, ubuntu-latest)	26m 43s
test (1.6, short, ubuntu-latest)	1h 32m 35s
doctest (1.11-nightly, ubuntu-latest)	26m 4s
test (1.6, long, ubuntu-latest)	53m 46s
doctest (nightly, ubuntu-latest)	5m 52s
test (1.10, short, ubuntu-latest)	1h 10m 39s
doctest (1.10, ubuntu-latest, depwarn=error)	26m 40s
test (1.10, long, ubuntu-latest)	43m 39s
doctest (1.10, macOS, RPTU)	12m 34s
test (1.11-nightly, short, ubuntu-latest)	1h 22m 31s
test (1.11-nightly, long, ubuntu-latest)	52m 27s
test (nightly, short, ubuntu-latest)	6m 36s
test (nightly, long, ubuntu-latest)	1h 5m 54s
test (1.10, short, ubuntu-latest, depwarn=error)	1h 10m 2s
test (1.10, long, ubuntu-latest, depwarn=error)	44m 0s
test (1.10, short, macOS, RPTU)	14m 8s
test (1.10, long, macOS, RPTU)	14m 19s
test (1.10, book, ubuntu-latest)	50m 0s
test (nightly, book, ubuntu-latest)	1h 6m 5s
	13h 44m 34s

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