fix: correct example to avoid zerolog fields combined

[levanlongktmt]

I follow the current code in the example of using zerolog and fields grown after each request. It combines all fields to the context of l after each request and makes the log messages become huge.
It's the same with this issue on zap #559

I fixed this by creating a new instance of zerolog.Logger instead of using l and it works like a charm.

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

• Correct example of interceptors/logging/examples/zerolog

Verification

I tested and it works on my project, logs work fine and didn't get combined fields

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[johanbrandhorst]

Thanks for the fix!