tests: sort import lines in failfilemerge.py

tests/failfilemerge.py

@@ -3,9 +3,9 b''
 from __future__ import absolute_import
 
 from mercurial import (
-    filemerge,
+    error,
     extensions,
-    error,
+    filemerge,
 )
 
 def failfilemerge(filemergefn,