Allow disabling Slither #2088

Job	Run time
Build Echidna on ubuntu-20.04	22m 11s
Build Echidna on ubuntu-20.04	22m 11s
Build Echidna on macos-13	28m 3s
Build Echidna on macos-13	28m 3s
Build Echidna on windows-latest	35m 17s
Build Echidna on windows-latest	35m 17s
Test with solc 0.4.25 on ubuntu-latest	3m 23s
Test with solc 0.4.25 on ubuntu-latest	3m 26s
Test with solc 0.5.7 on ubuntu-latest	3m 53s
Test with solc 0.5.7 on ubuntu-latest	4m 1s
Test with solc 0.6.12 on ubuntu-latest	3m 16s
Test with solc 0.6.12 on ubuntu-latest	3m 16s
Test with solc 0.7.5 on ubuntu-latest	3m 43s
Test with solc 0.7.5 on ubuntu-latest	3m 43s
Test with solc 0.4.25 on windows-latest	4m 25s
Test with solc 0.4.25 on windows-latest	4m 25s
Test with solc 0.5.7 on windows-latest	4m 12s
Test with solc 0.5.7 on windows-latest	3m 52s
Test with solc 0.6.12 on windows-latest	4m 22s
Test with solc 0.6.12 on windows-latest	4m 22s
Test with solc 0.7.5 on windows-latest	5m 8s
Test with solc 0.7.5 on windows-latest	5m 8s
	3h 55m 37s

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