Replace unmaintained GitHub Action - githubocto/flat

We have inventoried and assessed GitHub Actions used across all of our repositories.
We have flagged ones that are (1) no longer maintained (there hasn't been an update
in over a year), and (2) ones where their GitHub repositories have been archived and
are no longer receiving updates (security updates in particular).

The following GitHub Action in your repo is no longer being maintained/archived:

- githubocto/flat

There are 3 choices:

a. Reimplement the functionality with our own code
b. Find a suitable maintained alternative (https://github.com/bufbuild/buf-action is the replacement per the README.)
c. Fork it under the InfluxData organization and maintain it

Trivial functionality should be 'a' more complex is 'b'.
'c' would be a last resort since it means InfluxData must take on the maintenance of
a non-trivial project.

Search the repository's workflow files for githubocto/flat, then read the repository README and the linked bufbuild/buf-action documentation to compare the replacement's behavior. Update the affected workflow and confirm that the action is no longer referenced and the workflow remains valid.

Written by the indexing model from the issue text.