fix: use strings as webhook secrets

Fix https://codecov.sentry.io/share/issue/ef92212e1461452c90a16ae188e9c00b/

We were creating UUID4 webhook secrets per repo for gitlab and gitlab-enterprise.
When logging the body of the request the json decoder would crash.

tasks/upload.py

@@ -464,7 +464,7 @@ async def possibly_setup_webhooks(self, commit, repository_service):
             try:
                 if repository_service.service in ["gitlab", "gitlab_enterprise"]:
                     # we use per-repo webhook secrets in this case
-                    webhook_secret = repository.webhook_secret or uuid.uuid4()
+                    webhook_secret = repository.webhook_secret or uuid.uuid4().hex
                 else:
                     # service-level config value will be used instead in this case
                     webhook_secret = None