Add some sleep statements to give the "flush gc msgs" task enough time to finish

Author: DilumAluthge

stdlib/Distributed/test/distributed_exec.jl

@@ -143,6 +143,8 @@ function test_futures_dgc(id)
     @test fetch(f) == id
     @test f.v !== nothing
     yield(); # flush gc msgs
+    sleep(6);
+    yield();
     @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, fid) == false
 
 
@@ -153,6 +155,8 @@ function test_futures_dgc(id)
     @test f.v === nothing
     finalize(f)
     yield(); # flush gc msgs
+    sleep(6);
+    yield();
     @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, fid) == false
 end
 
@@ -243,6 +247,8 @@ function test_remoteref_dgc(id)
     @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, rrid) == true
     finalize(rr)
     yield(); # flush gc msgs
+    sleep(6);
+    yield();
     @test remotecall_fetch(k->(yield();haskey(Distributed.PGRP.refs, k)), id, rrid) == false
 end
 test_remoteref_dgc(id_me)