`@SentryCheckIn` always starts a new trace

### Integration

sentry

### Java Version

any

### Version

8.27.1

### Steps to Reproduce

https://github.com/getsentry/sentry-java/blob/3699cd5331a4c334c1e8a4bd85aa8e399f5c4231/sentry-samples/sentry-samples-spring-boot-4/src/main/java/io/sentry/samples/spring/boot4/CustomJob.java#L14 creates a transaction.

https://github.com/getsentry/sentry-java/blob/4c4fed9ef005ffc3acaf460ed345c1e700fdeefe/sentry-spring-7/src/main/java/io/sentry/spring7/checkin/SentryCheckInAdvice.java#L91 starts a new trace.

Use our Spring Boot 4 sample to verify.

### Expected Result

`PropagationContext` trace ID matches the transactions trace ID.

### Actual Result

`PropagationContext` trace ID differs from the transactions trace ID.

This might not have any effect in practice because we should be using the span/transaction when retrieving the trace ID.