test-runner: only remove GLib timeout if it exists

There was a race condition here where the GLib timeout could have
fired but the test function returned successfully prior to the
end of the while loop. This would end up causing source_remove to
print a warning that the source did not exist.

Instead check if the timeout fired prior to removing it.

tools/test-runner

@@ -751,10 +751,12 @@ class Namespace:
 			try:
 				ret = func(*args)
 				if ret:
-					GLib.source_remove(timeout)
+					if not done.value:
+						GLib.source_remove(timeout)
 					return ret
 			except Exception as e:
-				GLib.source_remove(timeout)
+				if not done.value:
+					GLib.source_remove(timeout)
 				raise e
 
 			sleep(0.1)