oslogin_trustedca.pub causes etckeeper with bzr backend to fail

Hi,

Since #222 landed and released as part of `google-guest-agent` `20231004.02-0ubuntu1~20.04.3`, we've started to notice that `etckeeper` is failing. The issue is with when `etckeeper` is configured to use the `bzr` / `bazaar` backend and fails as follows:

> /etc/cron.daily/etckeeper:
> skipping /etc/ssh/oslogin_trustedca.pub (can't add file of kind 'fifo')
> bzr: ERROR: No changes to commit. Please 'bzr add' the files you want to commit, or use --unchanged to force an empty commit.
> run-parts: /etc/cron.daily/etckeeper exited with return code 3

> ubuntu@juju-9b9b35-2:~$ ls -la /etc/ssh/oslogin_trustedca.pub
> prw-r--r-- 1 root root 0 Jan 10 14:42 /etc/ssh/oslogin_trustedca.pub

Any chance we could revisit the location to this named pipe? Perhaps a better location for it would be under `/run` as it isn't configuration related?

Having it under `/run` also aligns with the rest of the system, e.g.:

> ubuntu@juju-9b9b35-2:/$ sudo find / -type p -ls
> 5 0 p--------- 1 ubuntu ubuntu 0 Mar 4 20:42 /run/user/1000/inaccessible/fifo
> 65 0 prw------- 1 root root 0 Aug 30 2023 /run/initctl
> 664 0 prw-rw-rw- 1 root root 0 Aug 30 2023 /run/cloud-init/hook-hotplug-cmd
> 788 0 prw------- 1 root root 0 Aug 30 2023 /run/systemd/inhibit/1.ref
> 309324 0 prw------- 1 root root 0 Mar 4 20:42 /run/systemd/sessions/41381.ref
> 8 0 p--------- 1 root root 0 Aug 30 2023 /run/systemd/inaccessible/fifo
> 18915 0 prw-r--r-- 1 root root 0 Jan 10 14:42 /etc/ssh/oslogin_trustedca.pub
> ubuntu@juju-9b9b35-2:/$

Thanks!