gopls/internal/regtest/codelens: set GOWORK=off for go mod vendor

We might be introducing vendoring for workspace mode. Set GOWORK=off
when running go mod vendor in a single module context to make sure it
has the right behavior and doesn't return an error.

For golang/go#60056

Change-Id: I703d74d579aec6e4dad86ca092e3651e0b2e4eb0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/499977
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>

gopls/internal/lsp/regtest/wrappers.go

@@ -270,6 +270,15 @@ func (e *Env) RunGoCommandInDir(dir, verb string, args ...string) {
 	}
 }
 
+// RunGoCommandInDirWithEnv is like RunGoCommand, but executes in the given
+// relative directory of the sandbox with the given additional environment variables.
+func (e *Env) RunGoCommandInDirWithEnv(dir string, env []string, verb string, args ...string) {
+	e.T.Helper()
+	if err := e.Sandbox.RunGoCommand(e.Ctx, dir, verb, args, env, true); err != nil {
+		e.T.Fatal(err)
+	}
+}
+
 // GoVersion checks the version of the go command.
 // It returns the X in Go 1.X.
 func (e *Env) GoVersion() int {

gopls/internal/regtest/codelens/codelens_test.go

@@ -201,7 +201,7 @@ require golang.org/x/hello v1.2.3
 		t.Run(fmt.Sprintf("Upgrade individual dependency vendoring=%v", vendoring), func(t *testing.T) {
 			WithOptions(ProxyFiles(proxyWithLatest)).Run(t, shouldUpdateDep, func(t *testing.T, env *Env) {
 				if vendoring {
-					env.RunGoCommandInDir("a", "mod", "vendor")
+					env.RunGoCommandInDirWithEnv("a", []string{"GOWORK=off"}, "mod", "vendor")
 				}
 				env.AfterChange()
 				env.OpenFile("a/go.mod")