Use latest version of GitHub Actions at seeding time. - #33

When seeding a repository (or updating a pre-existing one), make sure
the GitHub Actions referenced in the GitHub workflows (if GitHub
workflows are used at all) are (i) referenced using a commit ID rather
than a tag name, and (ii) the commit ID points to the latest released
version.

This is done by having a small helper class (GitHubHelper) that
encapsulates the required calls to the GitHub API to get the latest
release information for a given project, and exposing that helper class
to the templates, so that we can write the following in a template:

  ```yaml
  uses: actions/checkout@{{ gh.get_latest_release_sha("actions/checkout", "v7") }}
  ```

  If we can get the required informations from GitHub, this will yield

  ```yaml
  uses: actions/checkout@XXXXX # vX.Y.Z
  ```

where `vX.Y.Z` is the latest release for the `actions/checkout` project,
and `XXXXX` is the corresponding commit ID.

In the event we could _not_ get the latest release info, then this will
yield

  ```yaml
  uses: actions/checkout@v7
  ```

closes INCATools/ontology-development-kit#1346

This commit does two things:

First, it simplifies the handling of exceptions thrown by the requests
library. All such exceptions are derived from the single
RequestException class, so since we are not interested in distinguishing
between the various error conditions, we can simply catch
RequestException instead of trying to catch all the various subclasses.

Second, it deals with the possibility that we could receive a response
that is not strictly speaking an error (HTTP status code < 400), but
that does not contain what we need either (e.g. status code == 204).
This is probably highly unlikely, but if it does happen, we must not
enter into an infinite loop.

The `mhausenblas/mkdocs-deploy-gh-pages` action has not had a new
release since 2023, but there has been some fixes on the master branch
since then, so we need to use the master branch. We add a comment next
to the tag for that action to make that a bit clearer.