GHSA-F8HV-G549-HWG2 Weblate: SSRF via the webhook add-on using unprotected fetch_url()

Impact The webhook add-on did not utilize existing SSRF protection. Patches https://github.com/WeblateOrg/weblate/pull/18815 Workarounds Disabling the add-on would avoid misusing this. References Thanks to @Lihfdgjr for reporting this via GitHub...