go.mod: bump Pebble to 030afd266b2d

[jbowens]

Note this commit includes manual changes to use the new KeySchema configuration API.

Changes:

• 030afd26 colblk: use UnsafeOffsets.At2 in another instance
• b3993ff6 db: persist Experimental.EnableColumnarBlocks in OPTIONS file
• c719c4e5 db: support multiple KeySchemas

Release note: none.
Epic: none.

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[cockroach-teamcity]

This change is 

[jbowens]

The MVCC metamorphic tests failed 😬

[RaduBerinde]

I don't get it, we're not even enabling the new format.. I looked at the code around opts.Experimental.EnableColumnarBlocks again and it seems fine..

[RaduBerinde]

They pass with this patch to options.go:

                        case "comparer":
-                               o.Comparer, err = parseComparer(value)
+                               var comparer *Comparer
+                               comparer, err = parseComparer(value)
+                               if comparer != nil {
+                                       o.Comparer = comparer
+                               }