Fix access-token

[agbeltran]

the GA is failing for PRs (see #37 and #28) and we need to investigate and provide an access-token

[louise-davies]

I think this is due to those PRs coming in from forks, which means they don't have access to the encrypted secret (see https://docs.github.com/en/actions/reference/encrypted-secrets#using-encrypted-secrets-in-a-workflow). However, we only need the access token for publishing, which only happens once merged (and thus will definitely have the access token) so there should be a way to fix this issue for builds only

[louise-davies]

See enriikke/gatsby-gh-pages-action#27
aka we should either use the solution in that thread or switch to the main github pages action

[agbeltran]

thanks @louise-davies - this is now fixed 182232e