tests/test-diff-newlines.t

archival: force a `CompressionError` to bytes before passing to `error.Abort`

I'm not sure what changed before pytype 09-09-2021 (from 04-15-2021), but this
started getting flagged.

This fixes:

    File "/mnt/c/Users/Matt/hg/mercurial/archival.py", line 199, in taropen: Function bytestr.__init__ was called with the wrong arguments [wrong-arg-types]
             Expected: (self, ints: Iterable[int])
      Actually passed: (self, ints: tarfile.CompressionError)
      Attributes of protocol Iterable[int] are not implemented on tarfile.CompressionError: __iter__

Differential Revision: https://phab.mercurial-scm.org/D11472

  $ hg init

  $ "$PYTHON" -c 'open("a", "wb").write(b"confuse str.splitlines\nembedded\rnewline\n")'
  $ hg ci -Ama -d '1 0'
  adding a

  $ echo clean diff >> a
  $ hg ci -mb -d '2 0'

  $ hg diff -r0 -r1
  diff -r 107ba6f817b5 -r 310ce7989cdc a
  --- a/a	Thu Jan 01 00:00:01 1970 +0000
  +++ b/a	Thu Jan 01 00:00:02 1970 +0000
  @@ -1,2 +1,3 @@
   confuse str.splitlines
   embedded\r (no-eol) (esc)
  newline
  +clean diff