runtime/metrics: /gc/scan* metrics return zero

[mknyszek]

These new metrics, introduced in Go 1.21, always return zero due to an oversight (no dependency declared in the metrics definition). https://go.dev/cl/525595 fixes this.

[mknyszek]

@gopherbot please open a backport issue for Go 1.21.

This issue means that some new metrics just don't work, and there's no workaround. Although the severity of the issue is quite low, the fix is also very safe and includes a test.

[gopherbot]

Backport issue(s) opened: #62478 (for 1.21).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[gopherbot]

Change https://go.dev/cl/525595 mentions this issue: runtime/metrics: fix /gc/scan/* metrics

[gopherbot]

Change https://go.dev/cl/526116 mentions this issue: [release-branch.go1.21] runtime/metrics: fix /gc/scan/* metrics