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.