py3: use `%d` for int in % formatting stable

py3: use `%d` for int in % formatting

On Python 3, `%s` is an alias to `%b`, which requires that the object implements
`__bytes__()`, which is not the case for `int`.

--- a/hgext/convert/subversion.py	Mon Jun 15 03:30:24 2020 +0200
+++ b/hgext/convert/subversion.py	Mon Jun 15 03:34:23 2020 +0200
@@ -773,7 +773,7 @@
         self.convertfp.flush()
 
     def revid(self, revnum, module=None):
-        return b'svn:%s%s@%s' % (self.uuid, module or self.module, revnum)
+        return b'svn:%s%s@%d' % (self.uuid, module or self.module, revnum)
 
     def revnum(self, rev):
         return int(rev.split(b'@')[-1])