Full changelog for patch releases can be incorrect

[triffer]

Description
When we create a release, we add a full changelog, which is a collection of changes since the last releases.
We always use the last release tag as a comparison when we create a changelog for a release, but there are scenarios where this is not correct if we want to create a patch for a release but there is already a release for a version with a higher major or minor version.

There is a branch release-2.2 with versions 2.2.0 and 2.2.1.
There is a branch release-2.3 with the versions 2.3.0.
If we now create a version 2.2.2, the full change log will use version 2.3.0 as the starting point instead of 2.2.1.

We can control the change log creation using the Changelog since field of the Create release action. We should update the release documentation to make it obvious that should be set for patch releases.

Expected result
The full changelog always uses the correct tag for a release.

Actual result
The full changelog always uses the latest release.

Steps to reproduce
See Description

Troubleshooting