[PATCH 2 of 2 STABLE] pure: use string for another exception in the pure version of base85

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at octobus.net>
# Date 1573931315 -3600
#      Sat Nov 16 20:08:35 2019 +0100
# Branch stable
# Node ID be24b4e16e3ee629b57203682d66faa4933fae1c
# Parent  c9224e21c5650b5884a5f69536c593fda7ee5055
# EXP-Topic fix-py3-pure-b85
# Available At https://dev.heptapod.net/octobus/mercurial-devel/
#              hg pull https://dev.heptapod.net/octobus/mercurial-devel/ -r be24b4e16e3e
pure: use string for another exception in the pure version of base85

That message does not seems tested, but I am assuming that the same reasoning as
for the previous changeset applies.

diff --git a/mercurial/pure/base85.py b/mercurial/pure/base85.py
--- a/mercurial/pure/base85.py
+++ b/mercurial/pure/base85.py
@@ -70,7 +70,7 @@ def b85decode(text):
                     'bad base85 character at position %d' % (i + j)
                 )
         if acc > 4294967295:
-            raise ValueError(b'Base85 overflow in hunk starting at byte %d' % i)
+            raise ValueError('Base85 overflow in hunk starting at byte %d' % i)
         out.append(acc)
 
     # Pad final chunk if necessary