http2: confirm the test fix for golang/go#28762 was correct

Fixes golang/go#28762

Change-Id: I8d8b74cd8836bbed3116b334f6595225a8f0a36e
Reviewed-on: https://go-review.googlesource.com/c/151619Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

http2/server_test.go

@@ -2416,7 +2416,8 @@ func testRejectTLS(t *testing.T, max uint16) {
 
 func TestServer_Rejects_TLSBadCipher(t *testing.T) {
 	st := newServerTester(t, nil, func(c *tls.Config) {
-		c.MaxVersion = tls.VersionTLS12 // workaround for golang.org/issue/28762
+		// All TLS 1.3 ciphers are good. Test with TLS 1.2.
+		c.MaxVersion = tls.VersionTLS12
 		// Only list bad ones:
 		c.CipherSuites = []uint16{
 			tls.TLS_RSA_WITH_RC4_128_SHA,