Currently regex matches characters until latest appearance of """. Which leads to such bugs:

Adding ? to regex should fix that, but I don't how to test patched grammar. Here is the patch if someone wants to test it and submit MR:

diff --git a/grammar.js b/grammar.js
index c503e69..51ea8c9 100644
--- a/grammar.js
+++ b/grammar.js
@@ -279,7 +279,7 @@ module.exports = grammar({
       seq('$(', $._expression, ')'),
       seq('$', $.identifier)
     ),
-    verbatim_string: $=> /"""(.|\n)*"""/,
+    verbatim_string: $=> /""".*?"""/s,
 
     literal: $ => choice(
         $.boolean,

Also replaced (.|\n) with s regex option, which makes . to match newlines. It performs slightly faster according to regex101.com and is more idiomatic IMO.