Remove dummy NODE_AUTH_TOKEN export

[v-gowridurgad]

Description:
The action previously exported a dummy NODE_AUTH_TOKEN value (XXXXX-XXXXX-XXXXX-XXXXX) when no token was provided. While this didn't break OIDC flows, it could corrupt the user's .npmrc by injecting a non-functional token value into the environment, potentially causing confusing behavior during OIDC publish. This PR removes the dummy fallback and only exports NODE_AUTH_TOKEN when the user has explicitly set it.

Related issue:
#1440

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.