fix(log): custom marshaller produce invalid data

[julienrbrt]

Description

The custom marshaller for Stringer (case fmt.Stringer) introduced at #17205 (comment) produces invalid results for some log event.

Step to reproduce

$ simd start --log_level="*:info"
...
zerolog: could not write event: failed to unmarshal event: invalid character '\n' in string literal
zerolog: could not write event: failed to unmarshal event: invalid character '\n' in string literal
zerolog: could not write event: failed to unmarshal event: invalid character '\n' in string literal
zerolog: could not write event: failed to unmarshal event: invalid character '\n' in string literal
zerolog: could not write event: failed to unmarshal event: invalid character '\n' in string literal
zerolog: could not write event: failed to unmarshal event: invalid character '\n' in string literal
zerolog: could not write event: failed to unmarshal event: invalid character '\n' in string litera
...

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[julienrbrt]

Tagging v1.2.1 once this is merged.