Ensure strings when setting openmc.lib.Tally.scores

In using lists of containing integer reactions as
the scores, e.g.
```
t = openmc.lib.Tally()
t.scores = [901]
```
The setter would fail as the integers do not have an
encode method. This converts all incoming scores
to strings prior to passing values to the shared library.

openmc/lib/tally.py

@@ -319,7 +319,7 @@ class Tally(_FortranObjectWithID):
     @scores.setter
     def scores(self, scores):
         scores_ = (c_char_p * len(scores))()
-        scores_[:] = [x.encode() for x in scores]
+        scores_[:] = [str(x).encode() for x in scores]
         _dll.openmc_tally_set_scores(self._index, len(scores), scores_)
 
     @property