GitHub Actions: Improve release automation

[tofi86]

• do not merge fast-forward when mergin master back to development (387da2b)
• cache Maven dependencies between builds (621cd7d)
• do not push [maven-release-plugin] prepare for next development iteration on master but only on development (eba08c2)
• upload the CI distributables to our download server via SCP and patch all relevant (php) files and release.xml