Update src/heartbeat.jl

Co-authored-by: Steven G. Johnson <stevenj@mit.edu>

src/heartbeat.jl

@@ -24,11 +24,7 @@ function heartbeat_thread(heartbeat_addr::Cstring)
     end
     ret = ZMQ.lib.zmq_proxy(heartbeat, heartbeat, C_NULL)
     @static if VERSION ≥ v"1.9.0-DEV.1588" # julia#46609
-        # julia automatically "adopts" this thread because
-        # we entered a Julia cfunction.  We then have to enable
-        # a GC "safe" region to prevent us from grabbing the
-        # GC lock with the call to zmq_proxy, which never returns.
-        # (see julia#47196)
+        # leave safe region if zmq_proxy returns (when context is closed)
         ccall(:jl_gc_safe_leave, Int8, ())
     end
     return ret