Fix reproducibly failing seed for PeerSyncWithLeaderTest

PeerSyncWithLeaderTest has been flaky for some time, failing somewhere between 1 and 5% of runs going as far back as 2018 according to fucit.

Usually I'm unable to reproduce failures, but I found a seed this morning that fails (for me at least) 10 out of 10 times:

./gradlew :solr:core:test --tests "org.apache.solr.update.PeerSyncWithLeaderTest.test" -Ptests.jvms=12 "-Ptests.jvmargs=-XX:TieredStopAtLevel=1 -XX:+UseParallelGC -XX:ActiveProcessorCount=1 -XX:ReservedCodeCacheSize=120m" -Ptests.seed=53640FCB37714D82 -Ptests.file.encoding=US-ASCII

(Environment is Intel Xeon, MacOS Sonoma, Java 17)

We should take this opportunity to fix the flakiness, while it's reproducible.