Update supported go versions

Following our policy regarding supported go releases, change the
supported go versions to 1.19.* and 1.20.* with the release of go 1.20.
diff --git a/go.mod b/go.mod
index 30de9f5..5f2a2c8 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
 module github.com/apache/thrift
 
-go 1.18
+go 1.19