fix: ensure flux check returns non-zero exit code on failure

[h3nryc0ding]

Fixes #5220 by returning a non-zero exist code for failed checks.

[matheuscscp]

I'm not sure what's gonna happen now that we both log and return the error, would we see the error printed twice? Can you please test that? Maybe we need to remove the log.

[h3nryc0ding]

StatusChecker.Assess is used in three places with inconsistent error handling:

1. check.go
   

   flux2/cmd/flux/check.go

   Lines 215 to 217 in f0fecf7

   	if err := statusChecker.Assess(ref...); err != nil {
   	ok = false
   	}

   • Does not use the error

2. install.go
   

   flux2/cmd/flux/install.go

   Lines 279 to 281 in f0fecf7

   	if err := statusChecker.Assess(componentRefs...); err != nil {
   	return fmt.Errorf("install failed")
   	}

   • Uses the error

3. bootstrap_plain_git.go

   flux2/pkg/bootstrap/bootstrap_plain_git.go

   Lines 492 to 494 in f0fecf7

   	if err := checker.Assess(identifiers...); err != nil {
   	return err
   	}

   • Uses the error

This means either:

• At least one of the locations logs the error twice, or
• check.go is missing necessary logging or needs refactoring

[matheuscscp]

Yeah maybe we need some refactoring here... We're busy preparing for KubeCon EU next week, can you please ping us again after KubeCon? Thanks 🙏