l2geth: skip unused tests (#2408)

The tests include:
- `TestBoundedForkedSync62`
- `TestBoundedForkedSync63Full`
- `TestBoundedForkedSync63Fast`
- `TestBoundedForkedSync64Full`
- `TestBoundedForkedSync64Fast`
- `TestBoundedForkedSync64Light`

None of these tests cover code that we use in production.
These tests were flaky upstream and eventually fixed.
No major changes to this codebase are planned before
deprecating it.
Co-authored-by: Matthew Slipper <me@matthewslipper.com>

.changeset/lovely-pigs-return.md

+---
+'@eth-optimism/l2geth': patch
+---
+
+Skip unused tests in l2geth

l2geth/eth/downloader/downloader_test.go

@@ -666,6 +666,7 @@ func TestBoundedForkedSync64Fast(t *testing.T)  { testBoundedForkedSync(t, 64, F
 func TestBoundedForkedSync64Light(t *testing.T) { testBoundedForkedSync(t, 64, LightSync) }
 
 func testBoundedForkedSync(t *testing.T, protocol int, mode SyncMode) {
+	t.Skip("Unused in Optimism")
 	t.Parallel()
 
 	tester := newTester()