feat(ci): use solc-select for tox

[spencer-tb]

🗒️ Description

Adds a step toward deprecating the requirement of solc for EEST (using solc-select instead).

Tox passes after merging this into my origin main, check recent commits:
https://github.com/spencer-tb/execution-spec-tests

I personally have not used an "installed solc" for the past 3 months, and instead used solc-select.
Due to the latter I've kept these changes trailing in my local repo for running tox.

🔗 Related Issues

#461 - planning to split the latter into smaller PRs, this PR being one of them.

Future PRs will include the deprecation of solc completely in within EEST in favor of solc-select.

✅ Checklist

• All: Set appropriate labels for the changes.
• All: Considered squashing commits to improve commit history.
• All: Added an entry to CHANGELOG.md.
• All: Considered updating the online docs in the ./docs/ directory.
• Tests: All converted JSON/YML tests from ethereum/tests have been added to converted-ethereum-tests.txt.
• Tests: Included the type and version of evm t8n tool used to locally execute test cases: e.g., ref with commit hash or geth 1.13.1-stable-3f40e65.
• Tests: Ran mkdocs serve locally and verified the auto-generated docs for new tests in the Test Case Reference are correctly formatted.

[marioevz]

Looks really nice, IMO the less things we have to update directly in the CI workflow files, the better.