operation: pad the marginal gzip test past Go 1.26's stored block (#12352)

At BestSpeed, Go 1.26's flate writes 4000 random bytes plus a 300-byte
zero run as a stored block, so the gzip output was 28 bytes larger than
the input and the test failed its own precondition on the toolchain
go.mod pins. With 450 zero bytes the saving is 5.7% on Go 1.26 and 8.4%
on Go 1.27, inside the marginal range on both.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

weed/operation/needle_parse_test.go

@@ -120,7 +120,7 @@ func TestCreateNeedleFromRequest(t *testing.T) {
 }
 
 func TestUploadKeepsMarginalGzipUncompressed(t *testing.T) {
-	data := make([]byte, 4300)
+	data := make([]byte, 4450)
 	rand.New(rand.NewSource(1)).Read(data[:4000])
 	gzipped, _ := util.GzipData(data)
 	if len(gzipped) >= len(data) || len(gzipped)*10 < len(data)*9 {