use GitHub token by default

This is done by other actions too e.g.
https://github.com/peter-evans/create-pull-request/blob/5354f85616108575685a73a0ddd2f67c26a441c3/action.yml#L4-L6
and
https://github.com/astral-sh/setup-uv/blob/754a7d4c2dd3b94cafffb1601b919a5705eec389/action.yml#L21-L25

Author: eifinger

README.md

@@ -56,13 +56,18 @@ To pin the exact version:
 ```
 
 The action queries the GitHub API to fetch releases data, to avoid rate limiting,
-pass the default token with the `repo-token` variable:
+pass the default token with the `repo-token` variable. By default,
+the `GITHUB_TOKEN` secret is used, which is automatically provided by GitHub Actions.
+
+If the default
+[permissions for the GitHub token](https://docs.github.com/en/actions/security-for-github-actions/security-guides/automatic-token-authentication#permissions-for-the-github_token)
+are not sufficient, you can provide a custom GitHub token with the necessary permissions:
 
 ```yaml
 - name: Install Protoc
   uses: arduino/setup-protoc@v3
   with:
-    repo-token: ${{ secrets.GITHUB_TOKEN }}
+    repo-token: ${{ secrets.CUSTOM_GITHUB_TOKEN }}
 ```
 
 ## Enable verbose logging for a pipeline

action.yml

@@ -10,7 +10,7 @@ inputs:
     default: 'false'
   repo-token:
     description: 'GitHub repo token to use to avoid rate limiter'
-    default: ''
+    default: ${{ github.token }}
 outputs:
   version:
     description: 'Actual version of the protoc compiler environment that has been installed'