Fixes #34189
Otherwise, the test may intermittently fail on slow CI systems that have --timeout-factor= properly set.
It can be tested by running ./bld-cmake/test/functional/interface_zmq.py --timeout-factor=10 with this diff:
0diff --git a/src/validationinterface.cpp b/src/validationinterface.cpp
1index c7be6abc3a..b14cf2aee6 100644
2--- a/src/validationinterface.cpp
3+++ b/src/validationinterface.cpp
4@@ -166,2 +166,3 @@ void ValidationSignals::SyncWithValidationInterfaceQueue()
5 LOG_EVENT(fmt, local_name, __VA_ARGS__); \
6+ UninterruptibleSleep(45ms); \
7 event(); \
8diff --git a/test/functional/interface_zmq.py b/test/functional/interface_zmq.py
9index 6717007626..eee377daea 100755
10--- a/test/functional/interface_zmq.py
11+++ b/test/functional/interface_zmq.py
12@@ -176,3 +176,3 @@ class ZMQTest (BitcoinTestFramework):
13 for sub in subscribers:
14- sub.socket.set(zmq.RCVTIMEO, recv_timeout*1000)
15+ sub.socket.set(zmq.RCVTIMEO, int(recv_timeout * 1000))
16
17@@ -271,3 +271,3 @@ class ZMQTest (BitcoinTestFramework):
18 [(topic, address) for topic in ["hashblock", "hashtx"]],
19- recv_timeout=2) # 2 second timeout to check end of notifications
20+ recv_timeout=0.2) # 2 second timeout to check end of notifications
21 self.disconnect_nodes(0, 1)
Before this pull: Test fails with zmq.error.Again: Resource temporarily unavailable
After this pull: Test passes