vm-runner: Add extra logging when selecting L1 head

[ajsutton]

Description

Add extra logging to assist with tracking down some weird l1 head is 0 errors we keep getting in vm-runner.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.

Project coverage is 42.06%. Comparing base (7b53454) to head (4a91ae5).
Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
op-challenger/runner/runner.go	0.00%	5 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #14061      +/-   ##
===========================================
- Coverage    46.44%   42.06%   -4.38%     
===========================================
  Files          989      824     -165     
  Lines        83610    74303    -9307     
===========================================
- Hits         38834    31259    -7575     
+ Misses       41848    40283    -1565     
+ Partials      2928     2761     -167     

Flag	Coverage Δ
cannon-go-tests-32	?
cannon-go-tests-64	?
contracts-bedrock-tests	?

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Files with missing lines	Coverage Δ
op-challenger/runner/runner.go	0.00% <0.00%> (ø)

... and 174 files with indirect coverage changes