Fix an error with groupby value_counts and pandas 2.0.

dask/dataframe/groupby.py

@@ -1543,7 +1543,17 @@ def _single_agg(
             with check_numeric_only_deprecation():
                 meta = func(self._meta_nonempty, **chunk_kwargs)
 
-        columns = meta.name if is_series_like(meta) else meta.columns
+        if is_series_like(meta):
+            # in pandas 2.0, Series returned from value_counts have a name
+            # different from original object, but here, column name should
+            # still reflect the original object name
+            if func is _value_counts:
+                columns = self._meta.apply(pd.Series).name
+            else:
+                columns = meta.name
+        else:
+            columns = meta.columns
+
         args = [self.obj] + (self.by if isinstance(self.by, list) else [self.by])
 
         token = self._token_prefix + token