Chain time is inconsistent

[theref]

Environment information

• brownie Version: 1.18.1
• ganache-cli Version: 6.12.2 (ganache-core: 2.13.2)
• solc Version: 1.1.1
• Python Version: 3.9.10
• OS: osx

What was wrong?

When interacting with the chain.time() (eg, sleep, mine etc) the timings are inconsistent.
This can be easily demonstrated with:

from brownie import chain


def test_chain_time():
    for _ in range(100):
        now = chain.time()
        chain.sleep(100)
        chain.mine()
        then = chain.time()
        assert now + 100 == then

Running the above test in a fresh brownie project will fail, but only sporadically.

This is probably related to #709