runtime/metrics: /memory/classes/heap/unused:bytes spikes [1.22 backport]

[gopherbot]

@mknyszek requested issue #67019 to be considered for backport to the next 1.22 minor release.

@gopherbot Please open backport issues for Go 1.21 and Go 1.22.

This issue can cause spurious overflow in runtime metrics with no workaround.

[gopherbot]

Change https://go.dev/cl/584339 mentions this issue: [relase-branch.go1.22] runtime: update large object stats before freeSpan in sweep

[cagedmantis]

Approved as this is a bug with no workaround.

[gopherbot]

Closed by merging 3c96ae0 to release-branch.go1.22.