chore: add alpine:3.21 to expected namespaces

Signed-off-by: Will Murphy <[email protected]>

tests/quality/config.yaml

@@ -78,6 +78,7 @@ tests:
       - alpine:distro:alpine:3.18
       - alpine:distro:alpine:3.19
       - alpine:distro:alpine:3.20
+      - alpine:distro:alpine:3.21
       - alpine:distro:alpine:edge
       - nvd:cpe # alpine lists fixes to NVD entries, so NVD entries are also expected
     validations: