[release-branch.go1.25] Revert "errors: optimize errors.Join for single unwrappable errors"
This reverts CL 635115.
Reason for revert: The new behavior does not match the function documentation.
For #76961
Fixes #76973
Change-Id: If2450aa4efba28c7a12887a5b306c231a836e740
Reviewed-on: https://go-review.googlesource.com/c/go/+/731981
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
(cherry picked from commit
1b3db48db7afc3fe17440af28cdeac67a0d048f1)
Reviewed-on: https://go-review.googlesource.com/c/go/+/734520
Reviewed-by: Junyang Shao <shaojunyang@google.com>