[CI] testSyncerOnClosingShard fails with soft-deletes

[dnhatn]

Acquiring a searcher on a closing shard should not throw an IllegalStateException.

ERROR   0.09s J0 | PrimaryReplicaSyncerTests.testSyncerOnClosingShard <<< FAILURES!
   > Throwable #1: java.lang.IllegalStateException: store is already closed can't increment refCount current count [0]
   > 	at __randomizedtesting.SeedInfo.seed([DEF0367146BEAE7F:F882A03DC173841A]:0)
   > 	at org.elasticsearch.common.util.concurrent.AbstractRefCounted.alreadyClosed(AbstractRefCounted.java:69)
   > 	at org.elasticsearch.common.util.concurrent.AbstractRefCounted.incRef(AbstractRefCounted.java:40)
   > 	at org.elasticsearch.index.store.Store.incRef(Store.java:384)
   > 	at org.elasticsearch.index.engine.InternalEngine.acquireSearcher(InternalEngine.java:2000)
   > 	at org.elasticsearch.index.engine.InternalEngine.newChangesSnapshot(InternalEngine.java:2433)
   > 	at org.elasticsearch.index.engine.InternalEngine.readHistoryOperations(InternalEngine.java:490)
   > 	at org.elasticsearch.index.shard.IndexShard.getHistoryOperations(IndexShard.java:1643)
   > 	at org.elasticsearch.index.shard.PrimaryReplicaSyncer.resync(PrimaryReplicaSyncer.java:92)

Reproduce command:

./gradlew :server:test \
  -Dtests.seed=DEF0367146BEAE7F \
  -Dtests.class=org.elasticsearch.index.shard.PrimaryReplicaSyncerTests \
  -Dtests.method="testSyncerOnClosingShard" \
  -Dtests.security.manager=true \
  -Dtests.locale=zh-CN \
  -Dtests.timezone=Africa/Cairo \
  -Dcompiler.java=10 \
  -Druntime.java=8

CI instances:

• https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+periodic/6960/console
• https://elasticsearch-ci.elastic.co/job/elastic+elasticsearch+master+matrix-java-periodic/ES_BUILD_JAVA=java11,ES_RUNTIME_JAVA=java8,nodes=virtual&&linux/274/console

[elasticmachine]

Pinging @elastic/es-distributed