Allow disabling Slither #2091

Job	Run time
Build Echidna on ubuntu-20.04	5m 37s
Build Echidna on ubuntu-20.04	5m 37s
Build Echidna on macos-13	36m 48s
Build Echidna on macos-13	36m 48s
Build Echidna on windows-latest	28m 57s
Build Echidna on windows-latest	28m 57s
Test with solc 0.4.25 on ubuntu-latest	3m 13s
Test with solc 0.4.25 on ubuntu-latest	3m 13s
Test with solc 0.5.7 on ubuntu-latest	3m 20s
Test with solc 0.5.7 on ubuntu-latest	3m 20s
Test with solc 0.6.12 on ubuntu-latest	4m 9s
Test with solc 0.6.12 on ubuntu-latest	4m 9s
Test with solc 0.7.5 on ubuntu-latest	3m 43s
Test with solc 0.7.5 on ubuntu-latest	3m 44s
Test with solc 0.4.25 on windows-latest	3m 39s
Test with solc 0.4.25 on windows-latest	3m 39s
Test with solc 0.5.7 on windows-latest	3m 42s
Test with solc 0.5.7 on windows-latest	3m 42s
Test with solc 0.6.12 on windows-latest	4m 25s
Test with solc 0.6.12 on windows-latest	4m 25s
Test with solc 0.7.5 on windows-latest	5m 25s
Test with solc 0.7.5 on windows-latest	5m 25s
	3h 25m 57s

Provide feedback