SOLR-16036 Race condition in SolrJmxReporterTest

[madrob]

https://issues.apache.org/jira/browse/SOLR-16036

[iamsanjay]

Race Condition!

 org.apache.solr.metrics.reporters.SolrJmxReporterTest.testClosedCore (:solr:core)
    Test history: https://ge.apache.org/scans/tests?search.rootProjectNames=solr-root&tests.container=org.apache.solr.metrics.reporters.SolrJmxReporterTest&tests.test=testClosedCore http://fucit.org/solr-jenkins-reports/history-trend-of-recent-failures.html#series/org.apache.solr.metrics.reporters.SolrJmxReporterTest.testClosedCore
    Test output: /home/jenkins/jenkins-slave/workspace/Solr/Solr-check-9.7/solr/core/build/test-results/test/outputs/OUTPUT-org.apache.solr.metrics.reporters.SolrJmxReporterTest.txt
    Reproduce with: ./gradlew :solr:core:test --tests "org.apache.solr.metrics.reporters.SolrJmxReporterTest.testClosedCore" -Ptests.jvms=4 -Ptests.haltonfailure=false "-Ptests.jvmargs=-XX:TieredStopAtLevel=1 -XX:+UseParallelGC -XX:ActiveProcessorCount=1 -XX:ReservedCodeCacheSize=120m" -Ptests.seed=D864F32CF202EEE8 -Ptests.multiplier=2 -Ptests.badapples=false -Ptests.file.encoding=UTF-8