Add spell check for modified files

[danieljurek]

The swift dictionary is not included by default in the pinned version of cspell that we're using: https://www.npmjs.com/package/@cspell/cspell-bundled-dicts/v/5.12.3

We'll either:

• Update to a newer set of bundled dictionaries globally (may cause new spelling error behavior) (preferred)
• Install and link this dictionary manually, either within the scope of this job (preferred) or in all runs (easier but adds time) (instructions)