Increase minimum Unity version to 20.3

Author: aurimasc

.yamato/upm-ci.yml

@@ -4,7 +4,6 @@ test_editors:
   - version: 2022.1
   - version: 2021.3
   - version: 2020.3
-  - version: 2019.4
 
 test_players:
   - version: trunk

com.unity.mobile.notifications/package.json

@@ -2,7 +2,7 @@
   "name": "com.unity.mobile.notifications",
   "displayName": "Mobile Notifications",
   "version": "2.0.2",
-  "unity": "2019.4",
+  "unity": "2020.3",
   "description": "Mobile Notifications package adds support for scheduling local repeatable or one-time notifications on iOS and Android.\n\nOn iOS receiving of push notifications is also supported.",
   "keywords": [
     "Android",