update ts6 to beta

Author: zloirock

tests/type-definitions/runner.mjs

@@ -14,7 +14,7 @@ const ES_TARGETS = [
 ];
 
 const TYPE_SCRIPT_VERSIONS = ALL_TESTS ? [
-  '6.0.0-dev.20260208',
+  '6.0.0-beta',
   '5.9',
   '5.8',
   '5.7',