Provide an input for github tokens (#172)

* Provide an input for github tokens

- By providing an input for github tokens with a default users no longer have to pass
  the github token via their environment across workflows.
- Remove GITHUB_TOKEN from our environment in all workflows

* Don't run workflows on main on pull requests

Co-authored-by: Paulo F. Oliveira <paulo.ferraz.oliveira@gmail.com>

action.yml

@@ -8,6 +8,15 @@ branding:
   color: blue
   icon: code
 inputs:
+  github-token:
+    description: >
+      A GitHub token used to access the GitHub REST API for retrieving release and version information.
+      While this action will never perform anything more than read operations against the GitHub REST API,
+      we do not recommend providing a self-generated personal access token which may provide more access than is
+      required of this action. This input instead is merely a convenience so that users of this action do not
+      have to manually pass an automatically generated token via their environment settings within a workflow.
+      [Learn more about automatically generated tokens](https://docs.github.com/en/actions/security-guides/automatic-token-authentication)
+    default: ${{ github.token }}
   otp-version:
     description: Version range or exact version of Erlang/OTP to use,
       or false when installing only Gleam without OTP