Fix Codecov for Go Tests

[tynes]

All of the Go unit tests should be uploading results to codecov so that we can make sure that code we are modifying is covered with tests. This will help with dev velocity if we integrate it into our daily workflow. Right now only cannon tests are included in codecov, you can see here: https://app.codecov.io/github/ethereum-optimism/optimism/tree/develop.

The codecov config file seems to be out of date: https://github.com/ethereum-optimism/optimism/blob/f2056c031ece39c681fa3e9e3690b958faf029fd/codecov.yml

The update needs to be made around here:

optimism/.circleci/config.yml

Line 915 in f2056c0

gotestsum --format=testname \