os/exec: calling Cmd.Start after setting Cmd.Path manually to absolute path without ".exe" no longer implicitly adds ".exe" in Go 1.22 [1.22 backport]

[gopherbot]

@rsc requested issue #66586 to be considered for backport to the next 1.22 minor release.

@gopherbot please backport go1.22

[gopherbot]

Change https://go.dev/cl/591397 mentions this issue: [release-branch.go1.22] os/exec: on Windows look for extensions in Run if not already done