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

mercurial/archival.py

@@ -29,6 +29,8 b' from . import ('
     vfs as vfsmod,
 )
 
+from .utils import stringutil
+
 stringio = util.stringio
 
 # from unzip source code:
@@ -196,7 +198,7 b' class tarit(object):'
                         name, pycompat.sysstr(mode + kind), fileobj
                     )
                 except tarfile.CompressionError as e:
-                    raise error.Abort(pycompat.bytestr(e))
+                    raise error.Abort(stringutil.forcebytestr(e))
 
         if isinstance(dest, bytes):
             self.z = taropen(b'w:', name=dest)