cmd/go: clean should respect workspaces

The existing implementation doesn't invoke modload.InitWorkfile during
runClean which in turn causes go clean to ignore workspaces and
consequentially workspace vendoring.

Fixes #74337

Change-Id: I295a1fcc5e81d096971c8cee9c9baa840c7725e7
Reviewed-on: https://go-review.googlesource.com/c/go/+/682856
Reviewed-by: Sam Thanawalla <[email protected]>
Auto-Submit: Sam Thanawalla <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>

Author: Acedus

src/cmd/go/internal/clean/clean.go

@@ -120,6 +120,7 @@ func init() {
 }
 
 func runClean(ctx context.Context, cmd *base.Command, args []string) {
+	modload.InitWorkfile()
 	if len(args) > 0 {
 		cacheFlag := ""
 		switch {