chore(deps): update ghcr.io/open-feature/flagd-testbed-unstable docker tag to v0.5.21 (#323)

Author: renovate[bot]

src/OpenFeature.Contrib.Providers.Flagd/docker-compose.yaml

@@ -4,7 +4,7 @@ services:
     ports:
       - 8013:8013
   flagd-unstable:
-    image: ghcr.io/open-feature/flagd-testbed-unstable:v0.5.6
+    image: ghcr.io/open-feature/flagd-testbed-unstable:v0.5.21
     ports:
       - 8014:8013
   flagd-sync: