Revert "remove check that GC queue must not be empty"

This reverts commit 4a772eb.

Author: MilesCranmer

test/GC.jl

@@ -5,6 +5,9 @@
             finalize(obj)
         end
     end
+    Threads.nthreads() > 1 &&
+        VERSION >= v"1.10.0-" &&
+        @test !isempty(PythonCall.GC.QUEUE.items)
     PythonCall.GC.gc()
     @test isempty(PythonCall.GC.QUEUE.items)
 end
@@ -16,6 +19,9 @@ end
             finalize(obj)
         end
     end
+    Threads.nthreads() > 1 &&
+        VERSION >= v"1.10.0-" &&
+        @test !isempty(PythonCall.GC.QUEUE.items)
     GC.gc()
     @test isempty(PythonCall.GC.QUEUE.items)
 end