Upgrade typescript config to target NodeJS 20

Fixes the error:

```
src/parsers/dart-json/dart-json-parser.ts:209:123 - error TS1501: This regular expression flag is only available when targeting 'es2018' or later.

209         /^══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞═+\s+(.*)\s+When the exception was thrown, this was the stack:/ms
```

package.json

@@ -77,5 +77,8 @@
     "suiteNameTemplate": "{filepath}",
     "classNameTemplate": "{classname}",
     "titleTemplate": "{title}"
+  },
+  "engines": {
+    "node": ">=20"
   }
 }