cmd/go: go generate fails silently when run on a package in a nested workspace module [1.22 backport]

[gopherbot]

@matloob requested issue #56098 to be considered for backport to the next 1.22 minor release.

@gopherbot please backport to 1.21 and 1.22. go generate doesn't work in workspace mode and it's a one-line fix

[gopherbot]

Change https://go.dev/cl/559236 mentions this issue: [release-branch.go1.22] cmd/go/internal/generate: call modload.InitWorkFile

[gopherbot]

Closed by merging b0957cf to release-branch.go1.22.