gopls/internal/cache: log go env in TestZeroConfigAlgorithm

Add an additional log message to help diagnose the problem encountered
by a user in golang/go#70196.

For golang/go#70196

Change-Id: I8347d842d5a9327fa6797229bf64dc4407f7aa61
Reviewed-on: https://go-review.googlesource.com/c/tools/+/625415
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Hongxiang Jiang <hxjiang@golang.org>
Auto-Submit: Robert Findley <rfindley@google.com>

gopls/internal/cache/session_test.go

@@ -340,12 +340,14 @@ replace (
 						t.Fatal(err)
 					}
 				}
-				env, err := FetchGoEnv(ctx, toURI(f.dir), opts)
+				uri := toURI(f.dir)
+				env, err := FetchGoEnv(ctx, uri, opts)
 				if err != nil {
 					t.Fatalf("FetchGoEnv failed: %v", err)
 				}
+				t.Logf("FetchGoEnv(%q) = %+v", uri, env)
 				folders = append(folders, &Folder{
-					Dir:     toURI(f.dir),
+					Dir:     uri,
 					Name:    path.Base(f.dir),
 					Options: opts,
 					Env:     *env,