Fix redundant newline in `show` for IncidenceMatrix #1116

Job	Run time
test (1.10, macos-14)	10m 54s
test-with-mongodb (~1.6.0-0, ubuntu-latest)	14m 26s
test (1.11, macos-14)	16m 55s
test-with-mongodb (~1.10.0-0, ubuntu-latest)	15m 59s
test (nightly, macos-14)	13m 5s
test-with-mongodb (1.11, ubuntu-latest)	30m 40s
test (macos-13, 1.6)	18m 7s
test-with-mongodb (nightly, ubuntu-latest)	14m 47s
	2h 14m 53s

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