Fix race condition bug during local session repair

The in-JVM dtest RepairErrorsTest#testNoSuchRepairSessionAnticompaction seems to be flaky, as it's shown by this repeated run on trunk, which hits 18 failures in 500 iterations. The config for CircleCI was generated with:

.circleci/generate.sh -m \
  -e REPEATED_UTEST_TARGET=test-jvm-dtest-some \
  -e REPEATED_UTEST_COUNT=500 \
  -e REPEATED_UTEST_CLASS=org.apache.cassandra.distributed.test.RepairErrorsTest

This was discovered while testing CASSANDRA-16878, on this CI run.

The error consists on a failed assertion when grepping the logs in search of an error message.