Update docker/dockerfile Docker tag to v1.9

| datasource | package           | from | to  |
| ---------- | ----------------- | ---- | --- |
| docker     | docker/dockerfile | 1.6  | 1.9 |


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

tests/Dockerfile

@@ -1,3 +1,3 @@
-# syntax=docker/dockerfile:1.6
+# syntax=docker/dockerfile:1.9
 # this is here so we can grab the latest version of the collector and have dependabot keep it up to date
 FROM otel/opentelemetry-collector-contrib:0.107.0