Fix possible deadlock in iresearch thread pool (#15372)
Fix possible deadlock in iresearch thread pool (#15372)

Co-authored-by: MBkkt <f6dfa1ede9040e29975e1978bf430dc5a619762d@gmail.com>
arangodb/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,arangodb/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,arangodb/arangodb,wiltonlazary/arangodb,arangodb/arangodb,wiltonlazary/arangodb,wiltonlazary/arangodb,arangodb/arangodb,arangodb/arangodb,arangodb/arangodb,wiltonlazary/arangodb,arangodb/arangodb