release-21.1: vendor: bump Pebble to 8f481c86fe98

[jbowens]

8f481c8 db: write manifest before creating WAL during Open
336bb5c internal/errorfs: allow more granular error injection

Release note(bug fix): Fix an issue where terminating a CockroachDB
process early in its startup routine might cause it fail to start again,
falsely reporting write-ahead log corruption.

Release justification: Fixes a critical issue that may cause a node to
fail to start.

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[itsbilal]

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @sumeerbhola)

[jbowens]

TFTR!

bors r=itsbilal

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @sumeerbhola)

[jbowens]

bors cancel

[craig]

Canceled.