jetstack/letsencrypt-caa-bug-checker: main.go; 20 LoC

Found a possible issue in [jetstack/letsencrypt-caa-bug-checker](https://www.github.com/jetstack/letsencrypt-caa-bug-checker) at [main.go](https://github.com/jetstack/letsencrypt-caa-bug-checker/blob/1acffa34afb2eb0858c16a24cf5d8a40bae8ab68/main.go#L153-L172)

Below is the message reported by the analyzer for this snippet of code. Beware that the analyzer only reports the first
issue it finds, so please do not limit your consideration to the contents of the below message.

> function call which takes a reference to req at line 156 may start a goroutine

[Click here to see the code in its original context.](https://github.com/jetstack/letsencrypt-caa-bug-checker/blob/1acffa34afb2eb0858c16a24cf5d8a40bae8ab68/main.go#L153-L172)

Click here to show the 20 line(s) of Go which triggered the analyzer.

```go
for _, req := range requests.Items {
// If any existing CertificateRequest resources exist and are complete,
// we delete them to avoid a re-issuance of the same certificate.
if !metav1.IsControlledBy(&req, &cert) {
continue
}

// This indicates an issuance is currently in progress
if len(req.Status.Certificate) == 0 {
log.Printf("Found existing CertificateRequest %s/%s for Certificate - skipping triggering a renewal...", req.Namespace, req.Name)
return nil
}

if err := cl.Delete(ctx, &req); err != nil {
log.Printf("Failed to delete old CertificateRequest %s/%s for Certificate", req.Namespace, req.Name)
return err
}

log.Printf("Deleted old CertificateRequest %s/%s for Certificate", req.Namespace, req.Name)
}

```

Leave a reaction on this issue to contribute to the project by classifying this instance as a **Bug** :-1:, **Mitigated** :+1:, or **Desirable Behavior** :rocket:
See the descriptions of the classifications [here](https://github.com/github-vet/rangeclosure-findings#how-can-i-help) for more information.

commit ID: 1acffa34afb2eb0858c16a24cf5d8a40bae8ab68