Update docker/dockerfile Docker tag to v1.9 (#822)

| datasource | package           | from | to  |
| ---------- | ----------------- | ---- | --- |
| docker     | docker/dockerfile | 1.8  | 1.9 |

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

build/Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.8
+# syntax=docker/dockerfile:1.9
 FROM golang:1.23 AS base
 ARG VERSION
 ARG TARGETARCH