Fix step values for susceptibility slider #195

Job	Run time
Ex1 (3.8, ubuntu-latest, tests/test_dcip.py)	36m 35s
Ex1 (3.8, ubuntu-latest, tests/test_em.py)	2h 22m 1s
Ex1 (3.8, ubuntu-latest, tests/test_gpr.py tests/test_seismic.py)	4h 5m 50s
Ex1 (3.8, ubuntu-latest, tests/test_inversion.py)	1h 10m 31s
Ex1 (3.8, ubuntu-latest, tests/test_gravity.py tests/test_mag.py)	35m 39s
Ex1 (3.10, ubuntu-latest, tests/test_dcip.py)	1m 29s
Ex1 (3.10, ubuntu-latest, tests/test_em.py)	1h 11m 56s
Ex1 (3.10, ubuntu-latest, tests/test_gpr.py tests/test_seismic.py)	3h 30m 42s
Ex1 (3.10, ubuntu-latest, tests/test_inversion.py)	32s
Ex1 (3.10, ubuntu-latest, tests/test_gravity.py tests/test_mag.py)	35m 44s
	14h 10m 59s

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