Describe the bug

If metrics are recevied then the traces are not serialized anymore in the output files.

To Reproduce
Steps to reproduce the behavior:

1. ./target/release/weaver registry live-check --inactivity-timeout=15 --no-stats --format=json --output foo
2. Send traces and metrics from instrumented application
3. In the foo/live_check.json I have only metrics

If I disable sending metrics from the instrumented application I see the traces.

Expected behavior

In the foo/live_check.json I have both metrics and traces

Additional context

Current git hash is ea50701

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