chore: default to internal actions token (#86)

## Overview

Most common actions needing the standard GitHub actions token set the
default behind the scenes.

README.md

@@ -32,6 +32,10 @@ on:
   pull_request:
   merge_group:
 
+permissions:
+  contents: read
+  checks: read
+
 jobs:
   sloth:
     runs-on: ubuntu-22.04

action.yml

@@ -6,7 +6,8 @@ branding:
 inputs:
   token:
     description: "GitHub token to use to interact with the GitHub API."
-    required: true
+    default: "${{ github.token }}"
+    required: false
   ref:
     description: "Git reference to inspect check runs for. The default supports Pull Requests, Merge Queues as well as branch pushes."
     required: false