[#142] Sort the columns in exploded_df_a and exploded_df_b when selec…

…ting them out

Previously we were selecting with a set, so the columns got all mixed up. Let's
sort them so that they are easier to work with. The order of the columns should
not affect the results.

hlink/linking/matching/link_step_explode.py

@@ -153,7 +153,7 @@ def _explode(
         # be a breaking change to remove this. We'd have to look into the
         # ramifications.
         if len(all_exploding_columns) > 0:
-            exploded_df = exploded_df.select(*all_column_names)
+            exploded_df = exploded_df.select(sorted(all_column_names))
 
         return exploded_df