encoding/gob: adding missing fuzz skip to one of the fuzz tests

It's slow & often times out randomly on longtest builders. Not useful.

Fixes #31517

Change-Id: Icedbb0c94fbe43d04e8b47d5785ac61c5e2d8750
Reviewed-on: https://go-review.googlesource.com/c/go/+/174522
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/encoding/gob/codec_test.go

@@ -1421,8 +1421,7 @@ func encFuzzDec(rng *rand.Rand, in interface{}) error {
 // This does some "fuzz testing" by attempting to decode a sequence of random bytes.
 func TestFuzz(t *testing.T) {
 	if !*doFuzzTests {
-		t.Logf("disabled; run with -gob.fuzz to enable")
-		return
+		t.Skipf("disabled; run with -gob.fuzz to enable")
 	}
 
 	// all possible inputs
@@ -1441,8 +1440,7 @@ func TestFuzz(t *testing.T) {
 
 func TestFuzzRegressions(t *testing.T) {
 	if !*doFuzzTests {
-		t.Logf("disabled; run with -gob.fuzz to enable")
-		return
+		t.Skipf("disabled; run with -gob.fuzz to enable")
 	}
 
 	// An instance triggering a type name of length ~102 GB.
@@ -1465,6 +1463,10 @@ func testFuzz(t *testing.T, seed int64, n int, input ...interface{}) {
 // TestFuzzOneByte tries to decode corrupted input sequences
 // and checks that no panic occurs.
 func TestFuzzOneByte(t *testing.T) {
+	if !*doFuzzTests {
+		t.Skipf("disabled; run with -gob.fuzz to enable")
+	}
+
 	buf := new(bytes.Buffer)
 	Register(OnTheFly{})
 	dt := newDT()