Duplicate key workflow_id in the agent logs

[hg]

Noticed this while studying logs in IDEA, which highlights these things:

{"level":"debug","repo":"demo/test","pipeline":"26","workflow_id":"184","image":"docker.io/woodpeckerci/plugin-git:2.5.2","workflow_id":"184","time":"2024-08-16T12:14:00Z","caller":"woodpecker/agent/logger.go:51","message":"log stream opened"}
{"level":"debug","repo":"demo/test","pipeline":"26","workflow_id":"184","image":"docker.io/woodpeckerci/plugin-git:2.5.2","workflow_id":"184","time":"2024-08-16T12:14:01Z","caller":"woodpecker/agent/logger.go:58","message":"log stream copied, close ..."}

The logger is built from another logger that already sets this field to the same value.

[woodpecker-bot]

Tearing down https://woodpecker-ci-woodpecker-pr-4046.surge.sh

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 26.83%. Comparing base (289f530) to head (1828a28).
Report is 14 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4046      +/-   ##
==========================================
- Coverage   26.88%   26.83%   -0.06%     
==========================================
  Files         396      394       -2     
  Lines       27465    27338     -127     
==========================================
- Hits         7384     7335      -49     
+ Misses      19376    19305      -71     
+ Partials      705      698       -7     

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