bundlerepo: use suffix variable

It looks like the refactor in 702a26fec3e2 attempted to establish
this method argument but failed to use it. My editor caught it.

Differential Revision: https://phab.mercurial-scm.org/D1373

mercurial/bundlerepo.py

@@ -321,7 +321,7 class bundlerepository(localrepo.localre
         """Write a temporary file to disk
         """
         fdtemp, temp = self.vfs.mkstemp(prefix="hg-bundle-",
-                                        suffix=".hg10un")
+                                        suffix=suffix)
         self.tempfile = temp
 
         with os.fdopen(fdtemp, pycompat.sysstr('wb')) as fptemp: