Doctests should only run in merge queue

[omus]

The doctests may require access to AWS resources. As forks will not have access to the secrets required for this in PRs we should ensure the doctests are run in the merge queue. We should still build the docs in the PR.

Noticed in #720

[omus]

Related to #725. We could run some doctests in the PR but we would need to indicate which require OIDC access