Fix required_status_checks syntax

[stephanme]

• branchprotector requires required_status_checks.contexts: [...]
• haproxy-boshrelease and pcap-boshrelease

[stephanme]

Should fix https://github.com/cloudfoundry/community/actions/runs/5541719611/jobs/10115492680

{"component":"branchprotector","error":"error unmarshaling branchprotection.out.yml: error unmarshaling JSON: while decoding JSON: json: cannot unmarshal array into Go struct field Repo.branch-protection.orgs.repos.required_status_checks of type config.ContextPolicy","file":"k8s.io/test-infra/prow/cmd/branchprotector/protect.go:114","func":"main.main","level":"fatal","msg":"Failed to load --config-path=branchprotection.out.yml","severity":"fatal","time":"2023-07-13T13:33:22Z"}