fix: add default ua egg-mock/${version}

[killagu]

superagent not set default ua.

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[codecov]

Codecov Report

Base: 82.88% // Head: 85.04% // Increases project coverage by +2.16% 🎉

Coverage data is based on head (14fdcf4) compared to base (9a5fcca).
Patch coverage: 87.93% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #151      +/-   ##
==========================================
+ Coverage   82.88%   85.04%   +2.16%     
==========================================
  Files          27       27              
  Lines        2465     2515      +50     
  Branches      409      444      +35     
==========================================
+ Hits         2043     2139      +96     
+ Misses        422      376      -46     

Impacted Files	Coverage Δ
lib/inject_context.js	89.79% <86.00%> (-4.09%)	⬇️
app/middleware/cluster_app_mock.js	91.46% <100.00%> (ø)
lib/mock_agent.js	100.00% <100.00%> (ø)
lib/request_call_function.js	62.50% <100.00%> (-1.50%)	⬇️
lib/supertest.js	100.00% <100.00%> (ø)
lib/app.js	97.94% <0.00%> (+1.02%)	⬆️
lib/cluster.js	95.07% <0.00%> (+2.02%)	⬆️
app/extend/application.js	95.62% <0.00%> (+9.40%)	⬆️

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[github-actions]

🎉 This PR is included in version 5.10.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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