Ease solc requirements in code coverage for new versions

[kanej]

Hardhat coverage depends on instrumenting code, this is done by Slang under the hood. Slang has a support version list. If a new version of solc is released, coverage will fail with an unsupported version error.
We should consider loosening this rule. If the code can be parsed with the latest version of solc (when a specific version isn't available) we should proceed with the instrumentation.