[tests/postprocessor] fix 'TypeError' when logging an error (#6582)

https://github.com/mikf/gallery-dl/issues/6582#issuecomment-3121493719

gallery_dl/version.py

@@ -6,5 +6,5 @@
 # it under the terms of the GNU General Public License version 2 as
 # published by the Free Software Foundation.
 
-__version__ = "1.30.1"
+__version__ = "1.30.2-dev"
 __variant__ = None

test/test_postprocessor.py

@@ -314,6 +314,7 @@ class ExecTest(BasePostprocessorTest):
 
         with patch("gallery_dl.util.Popen") as p:
             i = Mock()
+            i.wait.return_value = 0
             p.return_value = i
             self._trigger(("after",))
 
@@ -334,6 +335,7 @@ class ExecTest(BasePostprocessorTest):
 
         with patch("gallery_dl.util.Popen") as p:
             i = Mock()
+            i.wait.return_value = 0
             p.return_value = i
             self._trigger(("after",))