Switch from std to var in arm tutorial #2501

Job	Run time
benchmarks	1m 35s
coverage	1m 31s
examples	3m 2s
docs	2m 0s
pin	2m 48s
pre-commit	53s
test (ubuntu-latest, 3.12)	1m 24s
test (macos-latest, 3.12)	1m 41s
tutorials_list	3s
test (windows-latest, 3.12)	4m 23s
tutorials (tutorials/arm_repertoire.ipynb)	1m 30s
tutorials (tutorials/cma_mae.ipynb)	8m 6s
tutorials (tutorials/features/example.ipynb)	44s
tutorials (tutorials/fooling_mnist.ipynb)	4m 5s
tutorials (tutorials/lsi_mnist.ipynb)	9m 27s
tutorials (tutorials/lunar_lander.ipynb)	10m 31s
tutorials (tutorials/scalable_cma_mae.ipynb)	4m 37s
deploy	0s
	58m 20s

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