make sure to test against lowest unity version supported

Karl Henkel · Karl Henkel · commit 6bbf8484f131 · 2021-01-11T13:50:31.000-05:00
diff --git a/.yamato/promotion.yml b/.yamato/promotion.yml
@@ -1,4 +1,5 @@
 test_editors:
+  - version: 2018.3
   - version: 2018.4
   - version: 2019.4
   - version: 2020.1
