docs: add V7 ESM migration and NODE_AUTH_TOKEN behavior change (#1593)

Co-authored-by: gowridurgad <gowridurgad@gmail.com>

README.md

@@ -14,9 +14,12 @@ This action provides the following functionality for GitHub Actions users:
 
 ## What's new in V7
 
-The V7 edition of the action includes:
 - Migrated action internals to ESM for compatibility with latest `@actions/*` packages. No changes to action inputs, outputs, or behavior.
 
+### Breaking change
+
+- The dummy `NODE_AUTH_TOKEN` fallback has been removed, as it could unintentionally affect the generated `.npmrc` with a non-functional token. With this change, if `registry-url` is set without `NODE_AUTH_TOKEN`, legacy Yarn Classic (1.x) and older Node/npm versions may fail, and pnpm may warn. npm Trusted Publishing (OIDC) is not affected, since it does not use `NODE_AUTH_TOKEN`.
+
 ## Breaking changes in V6
 
 - Caching is now automatically enabled for npm projects when either the `devEngines.packageManager` field or the top-level `packageManager` field in `package.json` is set to `npm`. For other package managers, such as Yarn and pnpm, caching is disabled by default and must be configured manually using the `cache` input.
@@ -31,7 +34,7 @@ The V7 edition of the action includes:
 - Upgraded action from node20 to node24.
   > Make sure your runner is on version v2.327.1 or later to ensure compatibility with this release. [See Release Notes](https://github.com/actions/runner/releases/tag/v2.327.1)
 
-For more details, see the full release notes on the [releases page](https://github.com/actions/setup-node/releases/v5.0.0)
+For more details, see the full release notes on the [releases page](https://github.com/actions/setup-node/releases)
 
 ## Usage