chore(deps): pin ghcr.io/regclient/regsync docker tag to a9db2da

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

Dockerfile

@@ -10,7 +10,7 @@ COPY ./ ./
 
 RUN CGO_ENABLED=0 go build -o /go/bin/composesync -trimpath -ldflags="-s -w" .
 
-FROM ghcr.io/regclient/regsync:alpine
+FROM ghcr.io/regclient/regsync:alpine@sha256:a9db2da8f07588ffafbe7bcd74f27fe40997b9ce3ab53c46f8780727ca4d705e
 
 COPY --from=build /go/bin/composesync /usr/local/bin/