chore: update required node to >=20.19.0

@mongodb-js/oidc-plugin requires openid-client (a universal ESM
module) using `require()` in the dist. CJS style require for universal
ESMs are supported by default in node ^20.19.0 || ^22.12.0 || >=23.0.0.
Ref: https://www.npmjs.com/package/openid-client#fn-universal

For that reason it would be better to hint that we work best with
at-least 20.19.0 instead of what we have currently.

Author: himanshusinghs

package.json

@@ -78,6 +78,6 @@
     "zod": "^3.25.76"
   },
   "engines": {
-    "node": ">=20.10.0"
+    "node": ">=20.19.0"
   }
 }