[release-branch.go1.23] syscall: on exec failure, close pidfd

[release-branch.go1.23] syscall: on exec failure, close pidfd

For #69284
Fixes #69402

Change-Id: I6350209302778ba5e44fa03d0b9e680d2b4ec192
Reviewed-on: https://go-review.googlesource.com/c/go/+/611495
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: roger peppe <rogpeppe@gmail.com>
Reviewed-by: Tim King <taking@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
(cherry picked from commit 8926ca9c5ec3ea0b51e413e87f737aeb1422ea48)
Reviewed-on: https://go-review.googlesource.com/c/go/+/613616
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>