Add missing migration

lutris/migrations/migrate_steam_appids.py

@@ -0,0 +1,18 @@
+"""Set service ID for Steam games"""
+from lutris.database.games import PGA_DB, get_games, sql
+
+
+def migrate():
+    """Run migration"""
+    for game in get_games():
+        if not game["steamid"]:
+            continue
+        if game["runner"] and game["runner"] != "steam":
+            continue
+        print("Migrating Steam game %s" % game["name"])
+        sql.db_update(
+            PGA_DB,
+            "games",
+            {"service": "steam", "service_id": game["steamid"]},
+            {"id": game["id"]}
+        )