Avoid forking `rootScopes` for Reactor if current thread has NoOpScopes #5996

Job	Run time
system-test (sentry-samples-spring-boot-opentelemetry, true, true)	5m 33s
system-test (sentry-samples-spring-boot-jakarta, false, true)	4m 40s
system-test (sentry-samples-spring-boot-opentelemetry-noagent, false, true)	5m 11s
system-test (sentry-samples-spring-boot, false, true)	3m 1s
system-test (sentry-samples-spring-boot-opentelemetry, true, false)	5m 31s
system-test (sentry-samples-spring-boot-webflux-jakarta, false, true)	2m 49s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry-noagent, false, true)	5m 29s
system-test (sentry-samples-spring-boot-webflux, false, true)	2m 45s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry, true, true)	5m 36s
system-test (sentry-samples-console, false, true)	1m 19s
system-test (sentry-samples-logback, false, true)	1m 34s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry, true, false)	5m 26s
system-test (sentry-samples-spring-boot-4-webflux, false, true)	2m 57s
system-test (sentry-samples-jul, false, true)	1m 52s
system-test (sentry-samples-spring-boot-4-opentelemetry, true, true)	5m 37s
system-test (sentry-samples-spring-jakarta, false, true)	2m 39s
system-test (sentry-samples-spring, false, true)	2m 25s
system-test (sentry-samples-spring-boot-4-opentelemetry, true, false)	5m 30s
system-test (sentry-samples-spring-boot-4, false, true)	2m 35s
system-test (sentry-samples-log4j2, false, true)	1m 32s
system-test (sentry-samples-spring-7, false, true)	2m 27s
	1h 16m 28s

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