tests: add Python 3 output for test-remotefilelog-gc.t

Python 3 raises a slightly different error on invalid paths.

Differential Revision: https://phab.mercurial-scm.org/D5773

tests/test-remotefilelog-gc.t

@@ -108,5 +108,6 b''
 
   $ printf "asdas\0das" >> $CACHEDIR/repos
   $ hg gc
-  abort: invalid path asdas\x00da: stat() argument 1 must be encoded string without null bytes, not str (esc)
+  abort: invalid path asdas\x00da: stat: embedded null character in path (esc) (py3 !)
+  abort: invalid path asdas\x00da: stat() argument 1 must be encoded string without null bytes, not str (esc) (no-py3 !)
   [255]