op-node: Reduce log level for finalized block check

[palango]

Summary

• Reduces the log level from Warn to Debug for the "requested L1 block is beyond local finalized height" message in op-node/rollup/finalized/finalized.go
• This message fires frequently during normal operation and is not actionable, making it noise at the Warn level

Fixes #425

Test plan

• Existing tests in op-node/rollup/finalized/finalized_test.go continue to pass
• Verify reduced log noise in staging environment

[ezdac]

I'm not even sure what use there is for this log at all, especially in the generic fetcher method, just before returning an error.

I believe, that if at all, the log should be emitted in the caller, based on what it means for the caller.

In any case, this will significantly lower the current log noise we have.

[palango]

This was useful while building it, to see what requests are incoming.

The function overrides L1BlockRefByNumber and hides all non-confirmed blocks, so I think there are cases where this information might be useful.

[palango]

Failing CI is because I initially set the wrong target branch.