Fix step values for susceptibility slider #196

Job	Run time
Ex1 (3.8, ubuntu-latest, tests/test_dcip.py)	1h 11m 36s
Ex1 (3.8, ubuntu-latest, tests/test_em.py)	2h 21m 50s
Ex1 (3.8, ubuntu-latest, tests/test_gpr.py tests/test_seismic.py)	3h 30m 40s
Ex1 (3.8, ubuntu-latest, tests/test_inversion.py)	1h 10m 37s
Ex1 (3.8, ubuntu-latest, tests/test_gravity.py tests/test_mag.py)	35m 42s
Ex1 (3.10, ubuntu-latest, tests/test_dcip.py)	1m 35s
Ex1 (3.10, ubuntu-latest, tests/test_em.py)	1h 46m 57s
Ex1 (3.10, ubuntu-latest, tests/test_gpr.py tests/test_seismic.py)	4h 5m 54s
Ex1 (3.10, ubuntu-latest, tests/test_inversion.py)	44s
Ex1 (3.10, ubuntu-latest, tests/test_gravity.py tests/test_mag.py)	35m 40s
	15h 21m 15s

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