remotefilelog: fix logging in retry decorator

This still fails with an error about no exception being available to
re-raise, but so it goes.

Differential Revision: https://phab.mercurial-scm.org/D5600

hgext/remotefilelog/basestore.py

@@ -420,6 +420,7 b' class baseunionstore(object):'
                 except KeyError:
                     pass
             # retries exhausted
-            retrylog('retries exhausted in %s, raising KeyError\n' % funcname)
+            retrylog('retries exhausted in %s, raising KeyError\n' %
+                     pycompat.sysbytes(funcname))
             raise
         return wrapped