Remove @stoplight/spectral-rulesets pin once upstream null-crash fix ships

[hdamker]

Tracking issue to undo the temporary pin added in #329.

@stoplight/spectral-rulesets is pinned to 1.22.2 to avoid an upstream crash on null example values (Cannot read properties of null (reading 'enum')), a regression from stoplightio/spectral#2934.

Action when upstream releases a fix (track stoplightio/spectral#2959 / #2963):

1. Confirm the fixed spectral-rulesets version lints a null-containing spec cleanly.
2. Remove the @stoplight/spectral-rulesets entry from overrides in validation/package.json; npm install.
3. Run the validation regression; move @v1-rc.

Until then the pin stays. Latest release (1.22.4) still crashes.