fix: Do not set RebootTriggeredAt to nil too early

[guettli]

Summary

RebootTriggeredAt was set to nil to early.

Then hasJustRebooted() returned true forever when RebootTriggeredAt is nil but ErrorType is SSHRebootTriggered.

This was introduced in 4f9d7c6 in April this year:

        if s.scope.HetznerBareMetalHost.Spec.Status.ErrorType == infrav1.ErrorTypeConnectionError {
                s.scope.HetznerBareMetalHost.ClearError()
+               s.scope.HetznerBareMetalHost.Spec.Status.RebootTriggeredAt = nil
        }

How this state is reached

The exact path that produces ErrorType=SSHRebootTriggered with RebootTriggeredAt=nil:

1. During a reboot, the server becomes temporarily unreachable → handleIncompleteBoot sets ErrorType=ConnectionError, RebootTriggeredAt=<time>.
2. On the next reconcile the server is reachable again → lines 435–437 clear the connection error and set RebootTriggeredAt=nil.
3. SSH still times out (server hasn't fully rebooted yet) → the emptyErrorType case sets ErrorType=SSHRebootTriggered but (before this fix) never re-sets RebootTriggeredAt.
4. hasJustRebooted() sees SSHRebootTriggered + nil timestamp → hasTimedOut(nil, …) returns false → !false == true → stuck forever.

[janiskemper]

@guettli can you update the PR title and description again and also add a comment to the utility function you updated? Basically, I would say that this PR is about fixing a bug where we set RebootedAt too early to nil.

Keeping the change in the utility function wouldn't be necessary but might be a safe guard for the future.

[guettli]

@guettli can you update the PR title and description again and also add a comment to the utility function you updated? Basically, I would say that this PR is about fixing a bug where we set RebootedAt too early to nil.

Keeping the change in the utility function wouldn't be necessary but might be a safe guard for the future.

@janiskemper

PR title and description got updated.

In ec53299 I added a comment and log, when the value is nil, which is not expected.

[guettli]

Cherry-picked into release-1.1 via 240eaa5