SSLConfigurationReloaderTests hangs when run locally

[gwbrown]

This test suite hangs indefinitely when run locally, but I haven't seen CI be impacted yet.

Reproduce with:

./gradlew :x-pack:plugin:core:test \
  -Dtests.seed=5DB61DD425F081B \
  -Dtests.class=org.elasticsearch.xpack.core.ssl.SSLConfigurationReloaderTests \
  -Dtests.security.manager=true \
  -Dtests.locale=en-US \
  -Dtests.timezone=Etc/UTC

Whichever test runs first in this suite hangs.
Upon further investigation, only testReloadingTrustStore and testReloadingPEMTrustConfig hang.

Possibly related to #32124

Appears to have been introduced by #38103

Confirmed on MacOS and Linux.

[elasticmachine]

Pinging @elastic/es-security