refactor: simplify UError construction

[xtqqczze]

No description provided.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/misc/sleep. tests/misc/sleep is passing on 'main'. Maybe you have to rebase?
GNU test failed: tests/timeout/timeout-group. tests/timeout/timeout-group is passing on 'main'. Maybe you have to rebase?
Skip an intermittent issue tests/date/date-locale-hour (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/symlink (fails in this run but passes in the 'main' branch)
Congrats! The gnu test tests/rm/isatty is no longer failing!
Note: The gnu test tests/rm/many-dir-entries-vs-OOM is now being skipped but was previously passing.
Note: The gnu test tests/seq/seq-epipe is now being skipped but was previously passing.

[cakebaker]

Thanks!