fix: upgrade gatsby-source-wordpress from 7.0.0 to 7.15.0

Snyk has created this PR to upgrade gatsby-source-wordpress from 7.0.0 to 7.15.0.

See this package in npm:
gatsby-source-wordpress

See this project in Snyk:
https://app.snyk.io/org/sammytezzy/project/20794044-5f49-41de-a492-223de49c2642?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot