Upgrade build to GHC 9.6 #2010

Job	Run time
Build Echidna on ubuntu-20.04	22m 55s
Build Echidna on macos-13	38m 46s
Build Echidna on windows-latest	24m 27s
Test with solc 0.4.25 on ubuntu-latest	4m 40s
Test with solc 0.5.7 on ubuntu-latest	3m 12s
Test with solc 0.6.12 on ubuntu-latest	3m 26s
Test with solc 0.7.5 on ubuntu-latest	3m 32s
Test with solc 0.4.25 on windows-latest	3m 49s
Test with solc 0.5.7 on windows-latest	4m 23s
Test with solc 0.6.12 on windows-latest	3m 57s
Test with solc 0.7.5 on windows-latest	5m 2s
	1h 58m 9s

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