test(lib/util/http/host-rules.spec): refactor to use more `it` blocks

[jamietanna]

Describe the proposed change(s).

I've found that while editing this in:

• test(hostrules/github): add clearer precedence examples #38961
• chore(presets): add hostType=github to :githubComToken #38975

That it can be a little awkward with one big it block, especially if modifying state like hostRules