feat: use action input instead of env var to get the github token

BREAKING CHANGE: GITHUB_TOKEN env var is now ignored. In case a custom token is needed,
it'll be necessary to pass it via the `token` input from now on.

action.yml

@@ -7,7 +7,9 @@ inputs:
     default: './commitlint.config.js'
     required: false
   firstParent:
-    description: 'When set to true, we follow only the first parent commit when seeing a merge commit. More info in git-log docs https://git-scm.com/docs/git-log#Documentation/git-log.txt---first-parent'
+    description: >
+      When set to true, we follow only the first parent commit when seeing a merge commit.
+      More info in git-log docs https://git-scm.com/docs/git-log#Documentation/git-log.txt---first-parent
     default: 'true'
     required: false
   failOnWarnings:
@@ -18,6 +20,13 @@ inputs:
     description: 'Link to a page explaining your commit message convention'
     default: 'https://github.com/conventional-changelog/commitlint/#what-is-commitlint'
     required: false
+  token:
+    description: >
+      Personal access token (PAT) used to interact with the GitHub API.
+      By default, the automatic token provided by GitHub is used.
+      You can see more info about GitHub's default token here: https://docs.github.com/en/actions/configuring-and-managing-workflows/authenticating-with-the-github_token
+    default: ${{ github.token }}
+    required: false
 outputs:
   results:
     description: The error and warning messages for each one of the analyzed commits