[build] Some files required by make check aren't updated by make update

[faec]

As discovered in #26419, some files that can cause make check to fail aren't updated on make update, as in the following output:

Error: some files are not up-to-date. Run ‘make update’ then review and commit the changes. Modified: [filebeat/input/syslog/format_check.go]

filebeat/input/syslog/format_check.go is the only file where I've seen this so far, though there may be others. To reproduce, edit format_check.go and change the indentation level of some line so that it fails the linter; make update will leave it untouched but make check will fail (leaving a corrected file in place).

A workaround for this is to simply run make check instead of make update, but this is clearly not intentional or documented, so as long as we're still using make update we should keep its behavior in sync with the checks.

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!

[faec]

We really should have a build system that fits its own documentation for a command that is run on every checkin.

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!