fix(docs): add missing comma between properties in code example (#23859)
fix(docs): add missing comma between properties in code example (#23859)

* fix(docs): add missing comma to code example

## Description
Fixes an error within an example code block of the sourcing-from-sanity doc.
- Adds missing comma between properties of the 'gatsby-source-sanity' plugin options.

* chore: format

Co-authored-by: gatsbybot <313a651c59fdaade90d152972001707d94b0975c@gmail.com>
gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby