Use built-in core object in github-script example

Replace manual require of @actions/core with the built-in core object
that is automatically available in github-script action. This provides
a cleaner and more straightforward approach.

Reference: https://github.com/actions/github-script?tab=readme-ov-file#this-action

Author: ryohighbridge

content/actions/how-tos/secure-your-work/security-harden-deployments/oidc-in-cloud-providers.md

@@ -80,9 +80,8 @@ jobs:
       id: idtoken
       with:
         script: |
-          const coredemo = require('@actions/core')
-          let id_token = await coredemo.getIDToken()
-          coredemo.setOutput('id_token', id_token)
+          let id_token = await core.getIDToken()
+          core.setOutput('id_token', id_token)
 ```
 
 ### Requesting the JWT using environment variables