time,runtime: too many concurrent timer firings for short, fast-resetting `time.Timer` [1.23 backport]

[gopherbot]

@ianlancetaylor requested issue #69969 to be considered for backport to the next 1.23 minor release.

@gopherbot Please open backport to 1.23

Parts of the change that this fixes have been backported to 1.23. We should complete the backport so that 1.23 includes all the fixes.

[mknyszek]

I can't make a clean cherry-pick until https://go.dev/cl/620137 lands (waiting for approval on #69882).

[gopherbot]

Change https://go.dev/cl/621856 mentions this issue: [release-branch.go1.23] runtime,time: use atomic.Int32 for isSending

[gopherbot]

Closed by merging CL 621856 (commit 58babf6) to release-branch.go1.23.