Issue #18081: Workaround "./python -m test_idle test_logging" failure

"import idlelib" should not install hooks on the warning modules, hooks should
only be installed when IDLE is started.
diff --git a/Lib/idlelib/run.py b/Lib/idlelib/run.py
index 15f4472..74c1b89 100644
--- a/Lib/idlelib/run.py
+++ b/Lib/idlelib/run.py
@@ -40,7 +40,6 @@
             s += "    %s\n" % line
         s += "%s: %s\n" % (category.__name__, message)
         return s
-    warnings.formatwarning = idle_formatwarning_subproc
 
 
 tcl = tkinter.Tcl()
@@ -82,6 +81,9 @@
     global exit_now
     global quitting
     global no_exitfunc
+
+    warnings.formatwarning = idle_formatwarning_subproc
+
     no_exitfunc = del_exitfunc
     #time.sleep(15) # test subprocess not responding
     try: