test: fix matplotlib deprecations #1873

Job	Run time
build	30s
get-environments	11s
test (hatch-test.few-extras, 3.14)	5m 35s
test (hatch-test.pre, coverage, 3.14)	6m 37s
test (hatch-test.stable, 3.14)	6m 23s
test (hatch-test.low-vers, coverage, 3.12)	8m 34s
check	4s
	27m 54s

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