test: Add unregister_validation_interface_race test
test: Add unregister_validation_interface_race test

This commit is (intentionally) adding a broken test. The test is broken
because it registering a subscriber object that can go out of scope
while events are still being sent.

To run the broken test and reproduce the bug:
  - Remove comment /** and */
  - ./configure --with-sanitizers=address
  - export ASAN_OPTIONS=detect_leaks=0
  - make
  - while ./src/test/test_bitcoin -t validationinterface_tests/unregister_validation_interface_race --catch_system_errors=no  ; do true; done

Github-Pull: #18742
Rebased-From: fab6d060ce5f580db538070beec1c5518c8c777c

GroestlCoin/GroestlCoin,GroestlCoin/GroestlCoin,ahmedbodi/vertcoin,vertcoin/vertcoin,vertcoin/vertcoin,GroestlCoin/bitcoin,GroestlCoin/bitcoin,ahmedbodi/vertcoin,qtumproject/qtum,ahmedbodi/vertcoin,qtumproject/qtum,peercoin/peercoin,DigitalPandacoin/pandacoin,GroestlCoin/bitcoin,GroestlCoin/bitcoin,ahmedbodi/vertcoin,monacoinproject/monacoin,GroestlCoin/GroestlCoin,peercoin/peercoin,vertcoin/vertcoin,qtumproject/qtum,peercoin/peercoin,DigitalPandacoin/pandacoin,DigitalPandacoin/pandacoin,GroestlCoin/bitcoin,monacoinproject/monacoin,vertcoin/vertcoin,DigitalPandacoin/pandacoin,ahmedbodi/vertcoin,vertcoin/vertcoin,monacoinproject/monacoin,GroestlCoin/GroestlCoin,DigitalPandacoin/pandacoin,peercoin/peercoin,GroestlCoin/bitcoin,vertcoin/vertcoin,DigitalPandacoin/pandacoin,monacoinproject/monacoin,qtumproject/qtum,peercoin/peercoin,qtumproject/qtum,monacoinproject/monacoin,ahmedbodi/vertcoin,GroestlCoin/GroestlCoin,peercoin/peercoin,qtumproject/qtum,GroestlCoin/GroestlCoin,qtumproject/qtum,monacoinproject/monacoin