[release tool]: run nvm gracefully to ensure caretaker uses correct node version for publish branch

The merge tool will currently check out other branches, such as patch, LTS etc. For that the node versions could be different and breaking. This currently results in some inconvenient Yarn install engines error mid-publishing in a way where recovering is rather cumbersome..

We should run `nvm` automatically, gracefully as not everbody might have it. If it fails, we print a warning and proceed running the Yarn install. That one could still fail in such cases, but this is expected then.

Note: We have considered using the Bazel-managed Node version (that would be ideal).. but we cannot let Bazel install the node modules as Bazel itself is actually made available through the `@bazel/bazelisk` package (caretaker might not have the proper Bazel version globally installed; if at all)

Beginne beim Branch-Checkout und Yarn-Installationsablauf des Merge-Tools, insbesondere dort, wo das Publishing auf Patch- oder LTS-Branches wechselt. Prüfe, wie das Tool derzeit die Umgebung einrichtet, und verifiziere dann, dass nvm ordnungsgemäß versucht wird, dass Warnungen ausgegeben werden, wenn es nicht verfügbar ist oder fehlschlägt, und dass Yarn install weiterhin ausgeführt wird.

Vom Indexierungsmodell aus dem Issue-Text verfasst.