ci(acceptance-tests): enable debug logging for flake-shake gate

[scharissis]

Summary

• Adds --log.level debug to the flake-shake op-acceptor invocation in CI
• Previously no log level was set, so it used the default; this makes debug output explicit for better visibility into test failures

Test plan

• Verify flake-shake CI job produces debug-level logs on next scheduled run

[nonsense]

DEBUG log.level set as part of #19173

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.0%. Comparing base (e7fcac9) to head (7911bc3).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #19174     +/-   ##
==========================================
- Coverage     76.3%    76.0%   -0.4%     
==========================================
  Files          188      188             
  Lines        10946    10946             
==========================================
- Hits          8360     8325     -35     
- Misses        2440     2477     +37     
+ Partials       146      144      -2     

Flag	Coverage Δ
cannon-go-tests-64	66.4% <ø> (-0.9%)	⬇️
contracts-bedrock-tests	81.6% <ø> (-0.1%)	⬇️

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see 6 files with indirect coverage changes

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