tide status: do not post statuses on PRs in archived repos
tide status: do not post statuses on PRs in archived repos

The other controller filters out archived repo too. Archived repos are
read only so attempts to post statuses on PRs in archived repos end up
with 403:

```
Failed to set status context from "" to "error" and description from "" to "Not mergeable. PR has a merge conflict.", error=the GitHub API request returns a 403 error: {"message":"Repository was archived so is read-only."
```

jessfraz/test-infra,michelle192837/test-infra,cblecker/test-infra,monopole/test-infra,monopole/test-infra,cblecker/test-infra,monopole/test-infra,monopole/test-infra,cjwagner/test-infra,cjwagner/test-infra,cblecker/test-infra,fejta/test-infra,kubernetes/test-infra,dims/test-infra,cblecker/test-infra,monopole/test-infra,dims/test-infra,jessfraz/test-infra,dims/test-infra,monopole/test-infra,kubernetes/test-infra,michelle192837/test-infra,cblecker/test-infra,BenTheElder/test-infra,cjwagner/test-infra,cjwagner/test-infra,BenTheElder/test-infra,dims/test-infra,BenTheElder/test-infra,fejta/test-infra,michelle192837/test-infra,michelle192837/test-infra,fejta/test-infra,kubernetes/test-infra,cblecker/test-infra,jessfraz/test-infra,fejta/test-infra,kubernetes/test-infra,jessfraz/test-infra,fejta/test-infra,dims/test-infra,BenTheElder/test-infra,jessfraz/test-infra,BenTheElder/test-infra,kubernetes/test-infra,michelle192837/test-infra,kubernetes/test-infra,cjwagner/test-infra,jessfraz/test-infra,michelle192837/test-infra,dims/test-infra,fejta/test-infra,cjwagner/test-infra,BenTheElder/test-infra