Update spec tests to 1.6.0-alpha.3

[jimmygchen]

We're currently running 1.6.0-alpha.1

lighthouse/testing/ef_tests/Makefile

Line 3 in b08d49c

CONSENSUS_SPECS_TEST_VERSION ?= v1.6.0-alpha.1

For fusaka-devnet-3, we'll need to update the tests to work on 1.6.0-alpha.3

https://github.com/ethereum/consensus-spec-tests/releases/tag/v1.6.0-alpha.3

[eserilev]

im on it

[jimmygchen]

Completed in #7786, thanks @eserilev !