fix(test): Fix flaky MainEventProcessorTest by checking crashed thread #6997

Job	Run time
system-test (sentry-samples-spring-boot, false, true)	7m 19s
system-test (sentry-samples-spring-boot-opentelemetry, true, false)	10m 53s
system-test (sentry-samples-spring-boot-opentelemetry, true, true)	10m 36s
system-test (sentry-samples-spring-boot-webflux, false, true)	6m 18s
system-test (sentry-samples-spring-boot-opentelemetry-noagent, false, true)	10m 39s
system-test (sentry-samples-spring-boot-webflux-jakarta, false, true)	6m 33s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry, true, false)	8m 54s
system-test (sentry-samples-console, false, true)	4m 43s
system-test (sentry-samples-spring-boot-jakarta, false, true)	11m 25s
system-test (sentry-samples-log4j2, false, true)	4m 52s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry-noagent, false, true)	10m 50s
system-test (sentry-samples-spring-boot-4, false, true)	8m 38s
system-test (sentry-samples-spring-jakarta, false, true)	7m 59s
system-test (sentry-samples-spring, false, true)	6m 11s
system-test (sentry-samples-spring-boot-4-opentelemetry, true, false)	11m 32s
system-test (sentry-samples-spring-7, false, true)	8m 17s
system-test (sentry-samples-spring-boot-4-opentelemetry, true, true)	11m 6s
system-test (sentry-samples-jul, false, true)	4m 42s
system-test (sentry-samples-logback, false, true)	3m 18s
system-test (sentry-samples-spring-boot-4-webflux, false, true)	9m 57s
system-test (sentry-samples-spring-boot-jakarta-opentelemetry, true, true)	8m 53s
	2h 53m 35s

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