Add TruffleRuby 19.3.1

Author: eregon

README.md

@@ -13,7 +13,7 @@ This action currently supports these versions of MRI, JRuby and TruffleRuby:
 | ----------- | -------- |
 | Ruby | 2.3.0 - 2.3.8, 2.4.0 - 2.4.9, 2.5.0 - 2.5.7, 2.6.0 - 2.6.5, 2.7.0 |
 | JRuby | 9.2.9.0 |
-| TruffleRuby  | 19.3.0 |
+| TruffleRuby  | 19.3.0, 19.3.1 |
 
 The recommended way to refer to these versions is:
 `2.3`, `2.4`, `2.5`, `2.6`, `2.7`, `jruby`, `truffleruby`.