Adding Grammar and Spelling to Pull Request Checks

I've been trying to figure out what sort of tests are appropriate for this blog. I've finally remembered that grammar and spelling are important and initially looked at YaSpellerCI as an option, but finally found prosebot[bot] which performs grammar and spelling checks in addition to other writing suggestions.

The reason why I didn't use YaSpellerCI was because it only performs spelling checks, which is important, but probably less important.