fix(tests): EIP-6110: Add slow marker to many_deposits test

[marioevz]

🗒️ Description

Mark the many_deposits tests as slow due to timeouts that have been happening when filling using max parallelism.

🔗 Related Issues

None

✅ Checklist

• All: Set appropriate labels for the changes.
• All: Considered squashing commits to improve commit history.
• All: Added an entry to CHANGELOG.md. Skip.
• 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: A PR with removal of converted JSON/YML tests from ethereum/tests have been opened.
• 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.

[winsvega]

Is it disabled by default?

[marioevz]

Is it disabled by default?

Not really, but it's sometimes useful to use -m "not slow" if you want to quickly fill tests for local testing purposes.

It also increases the timeout from the t8n server for the marked test.