Add support for Debian 13 "trixie" - #1272

I think this would also need a file data/os/Debian/13.yaml to set the backports properly.

@Debilski good point, I updated it to make the Debian 12 and 13 settings the default, so that we don't have to keep copying the data for each new release.

Rebased the PR and will run some tests to get some acceptance testing feedback.

Running CI tests for this PR here: #1299

Acceptance Test Results: https://github.com/puppetlabs/puppetlabs-apt/actions/runs/37531348300?pr=1299

All green except for Debian 13 which failed on both Puppet Core 8 and Puppet Core 9:

• Puppet Core 8/Debian 13 results
• Puppet Core 9/Debian 13 results

Both had similar errors: Error: Could not find a suitable provider for apt_key

The Debian 13 failures in the CI run above (Could not find a suitable provider for apt_key) come from apt-key being removed in apt 3. #1337 addresses this for Ubuntu 26.04, following the deprecation approach discussed in #1306:

• apt_key and apt::key emit a deprecation warning.
• Where apt-key is missing, apt_key now fails with a clear error pointing to apt::keyring (or apt::source with key => { name => ..., source => ... }) instead of the provider error.
• The acceptance tests check for apt-key itself rather than the OS version: the apt-key-based examples skip, and new assertions check the error and the keyring alternative.

Because the check is based on whether apt-key exists, it should cover Debian 13 as well. Once #1337 is merged, rebasing this PR and re-running CI should show whether anything Debian 13-specific remains.