Flaky test: JvmThreadsMetricsTest.testInvalidThreadIds

[zeitlinger]

Description

JvmThreadsMetricsTest.testInvalidThreadIds is flaky — it counts threads
by state between two scrapes, but background threads (GC, JIT, etc.) can
start between the snapshots, causing a mismatch.

Seen on Java 17 CI:

expected: 6.0
 but was: 7.0

at line 139.

Suggested fix

Instead of comparing exact counts, compare the delta (or use
isGreaterThanOrEqualTo for states that can only grow).