Add scipy to test dependencies #1074

Job	Run time
linux-gallery-python3.13-optional	56s
windows-gallery-python3.13-optional	2m 8s
linux-gallery-python3.9-minimum	42s
windows-gallery-python3.9-minimum	1m 55s
conda-linux-python3.13	2m 29s
conda-linux-python3.13-optional	3m 47s
conda-linux-python3.9-minimum	2m 31s
linux-python3.13	2m 19s
linux-python3.13-optional	3m 31s
linux-python3.9-minimum	2m 7s
macos-python3.13	1m 32s
macos-python3.13-optional	3m 40s
macos-python3.9-minimum	2m 45s
windows-python3.13	4m 20s
windows-python3.13-optional	5m 8s
windows-python3.9-minimum	3m 54s
	43m 44s

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