[lint] Add Spell Check and Improve CI Lint Speed #check-lint-warning

Just adds a spellcheck linter to avoid the need to flag these manually in review. I fixed most spelling errors, but just added an ignore comment on the ones in error strings to avoid anything potentially consensus breaking.

This also makes a tweak to revert !2436 (merged) and only test changes on PRs, which should speed up lint a lot. It fixes the original issue that change intended to fix by explicitly fetching develop from origin instead of the repo-local branch.