Combine access token and pull request checks in workflow

[dskloetd]

This applies the changes from dfinity/snsdemo#380 (in snsdemo) to gix-components.

Motivation

EndBug/add-and-commit requires that the checkout action is called with ref, when used on a pull request, so it knows which branch to commit to. For some reason this was not required on older versions (7) of EndBug/add-and-commit.

In dfinity/snsdemo#368 I changed to an earlier version of EndBug/add-and-commit to avoid having to pass ref to the checkout action, depending on whether the run is for a PR, to avoid having to have 4 different checkout steps.
I realized now that I only need to pass the token if I plan to make changes, so I can combine the checkout steps and still only have 2 while also using newer versions of actions/checkout and EndBug/add-and-commit.

Changes

1. Check whether commits can be added based on both the presence of the PAT token and the even being for a PR.
2. Use actions/checkout@v4 and EndBug/add-and-commit@v9.1.4.

Tested

Was tested in the snsdemo repo but not separately tested in the gix-components repo.

[peterpeterparker]

Rubber stamp, thanks!