16770 work package api patch for subject

[``* `#16770` Work package API PATCH for subject``](https://community.openproject.org/work_packages/16770)

This PR applies the specified behavior outlined in #2056.
At the moment I cannot see how the change you propose would improve readability as [the code you reference](https://github.com/opf/openproject/pull/2081/files#diff-d5b7d1e80a5236e2a654ba407f1a8643R72) catches different kinds of system errors, which, I think, is not related. But don't hesitate to detail your idea.