tests/test-fuzz-targets.t

tests: allow [Errno] in output

I'm not sure why, but my system is printing "[Errno -5]" before
the "No address associated with hostname" message. I suspect a
modern version of Python improved errno tracking or something.

Add an "[Errno ...]" pattern as optional output to make the test
pass.

Differential Revision: https://phab.mercurial-scm.org/D1958

#require clang-libfuzzer test-repo
  $ cd $TESTDIR/../contrib/fuzz
  $ make
Just run the fuzzer for five seconds to verify it works at all.
  $ ./bdiff -max_total_time 5