chore(deps): update docker/dockerfile docker tag to v1.20 (#567)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [docker/dockerfile](https://redirect.github.com/moby/buildkit) |
syntax | minor | `1.19` -> `1.20` |

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docker/router.Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.19
+# syntax=docker/dockerfile:1.20
 
 FROM gcr.io/distroless/cc-debian12
 ARG TARGETARCH