fix: upgrade fastify from 4.20.0 to 4.21.0 (#308)

Snyk has created this PR to upgrade fastify from 4.20.0 to 4.21.0.

See this package in npm:
https://www.npmjs.com/package/fastify

See this project in Snyk:
https://app.snyk.io/org/nodeshift-agg/project/53f94480-e7ae-41d2-985c-270fae345664?utm_source=github&utm_medium=referral&page=upgrade-pr

Co-authored-by: snyk-bot <snyk-bot@snyk.io>

package.json

@@ -37,7 +37,7 @@
     "cloudevents": "^8.0.0",
     "commander": "^11.0.0",
     "death": "^1.1.0",
-    "fastify": "^4.20.0",
+    "fastify": "^4.21.0",
     "fastify-raw-body": "^4.2.1",
     "js-yaml": "^4.1.0",
     "node-os-utils": "^1.3.7",