Helm chart release workflow does not generate proper changelog

[ppawlowski]

When releasing a new version of the FlowFuse helm chart, a changelog should be generated with the changes between the last and second-to-last releases.
However, the current approach used for generating the diff does not consider squash commits. As a result, the changelog does not contain all the changes introduced in the release.

The goal of this task is to adjust the part of the release workflow responsible for generating the changelog so that it covers all changes introduced since the last release.