Fix ihs_gwss using wrong cache key "roh" instead of self._ihs_gwss_cache_name

Fixes #886. The ihs_gwss method was using a hardcoded cache name "roh"
(belonging to runs-of-homozygosity) instead of the class-defined
_ihs_gwss_cache_name property, risking silent cache collisions and
incorrect results being returned from the cache.

Author: blankkiri

malariagen_data/anopheles.py

@@ -1365,7 +1365,7 @@ def ihs_gwss(
     ) -> Tuple[np.ndarray, np.ndarray]:
         # change this name if you ever change the behaviour of this function, to
         # invalidate any previously cached data
-        name = "roh"
+        name = self._ihs_gwss_cache_name
 
         params = dict(
             contig=contig,