bind: Upgrade from 9.18 to 9.20 series

Bind uses even/odd series for stable/devel releases, with 9.20.x being
the latest stable and 9.21.x being the latest devel. Ideally we would
have "no-odd" semver flag in our update monitors; or jut a regexp
support for tag filtering.

Noticed via [OSS Security post](https://www.openwall.com/lists/oss-security/2024/12/21/1) about 9.20.4 critical issue.

bind.yaml

@@ -227,4 +227,4 @@ subpackages:
 update:
   enabled: true
   release-monitor:
-    identifier: 242117
+    identifier: 374094