Update to release process template to cut beta for screenshots

> - [ ] Finish App translations
> - [ ] Review translation PRs according to [release process checklist](https://jamulus.io/contribute/Release-Process#3-update-the-ts-files-returned-by-translators)
> - [ ] Wait for all PRs to be merged (missing translations will revert to English automatically).
> - [ ] Check for conflicting accelerator keys (see tools/checkkeys.pl)
> - [ ] Finish Website translations
> - [ ] Wait for all PRs to be merged (missing translations will revert to English automatically)
> - [ ] [Check for broken links](https://github.com/jamulussoftware/jamuluswebsite/blob/release/contribute/en/Release-Process.md#website-check-links)
>
> OK, so another thing we need to fix in the release process template is cutting another beta between `Finish App translations` and `Finish Website translations` so that the beta can be used for the screenshots.

_Originally posted by @pljones in [#3443](https://github.com/jamulussoftware/jamulus/issues/3443#issuecomment-3293182212)_

Beginne mit der im Issue verlinkten Checkliste für den Release-Prozess und finde den Template-Abschnitt, der die Übersetzungsschritte für App und Website enthält. Füge zwischen diesen Abschnitten einen beta-cut-Schritt ein, damit die Beta für Screenshots verwendet werden kann, und behalte dabei die bestehenden Übersetzungs- und tools/checkkeys.pl-Prüfungen bei.

Vom Indexierungsmodell aus dem Issue-Text verfasst.