runtime: memlock not unlocked in all control flow paths in sysReserveAlignedSbrk [1.24 backport]

[gopherbot]

@cherrymui requested issue #74339 to be considered for backport to the next 1.24 minor release.

@gopherbot please backport this to Go 1.24. This could potentially cause a deadlock. The fix is obviously safe. Thanks.

(1.24 only as sysReserveAlignedSbrk is new code in 1.24.)

[gopherbot]

Change https://go.dev/cl/684016 mentions this issue: [release-branch.go1.24] runtime: add missing unlock in sysReserveAlignedSbrk

[gopherbot]

Closed by merging CL 684016 (commit 1575127) to release-branch.go1.24.