chore(deps): update ghcr.io/open-feature/flagd-testbed-unstable docker tag to v0.5.1 (#679)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
           - 8013:8013
       # flagd-testbed for flagd RPC provider reconnect e2e tests
       flagd-unstable:
-        image: ghcr.io/open-feature/flagd-testbed-unstable:v0.5.0
+        image: ghcr.io/open-feature/flagd-testbed-unstable:v0.5.1
         ports:
           - 8014:8013
       # sync-testbed for flagd in-process provider e2e tests