cmd/go/internal/modfetch: update expected tags for TestCodeRepoVersions

Updates #28856

Change-Id: I89c564cefd7c5777904bc00c74617dab693373bf
Reviewed-on: https://go-review.googlesource.com/c/go/+/265819
Trust: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
diff --git a/src/cmd/go/internal/modfetch/coderepo_test.go b/src/cmd/go/internal/modfetch/coderepo_test.go
index 28c5e67..4364fef 100644
--- a/src/cmd/go/internal/modfetch/coderepo_test.go
+++ b/src/cmd/go/internal/modfetch/coderepo_test.go
@@ -648,7 +648,7 @@
 	{
 		vcs:      "git",
 		path:     "gopkg.in/russross/blackfriday.v2",
-		versions: []string{"v2.0.0", "v2.0.1"},
+		versions: []string{"v2.0.0", "v2.0.1", "v2.1.0-pre.1"},
 	},
 	{
 		vcs:      "git",