Update docker/dockerfile Docker tag to v1.19 (#8374)

| datasource | package           | from | to   |
| ---------- | ----------------- | ---- | ---- |
| docker     | docker/dockerfile | 1.18 | 1.19 |

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

Author: renovate[bot]

build/Dockerfile

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.18
+# syntax=docker/dockerfile:1.19
 ARG BUILD_OS=debian
 ARG NGINX_OSS_VERSION=1.29
 ARG NGINX_PLUS_VERSION=R35

build/dependencies/Dockerfile.ubi8

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.18
+# syntax=docker/dockerfile:1.19
 FROM redhat/ubi8@sha256:534c2c0efa4150ede18e3f9d7480d3b9ec2a52e62bc91cd54e08ee7336819619 AS rpm-build
 RUN mkdir -p /rpms/ \
     && dnf install rpm-build gcc make cmake -y \

build/dependencies/Dockerfile.ubi9

@@ -1,4 +1,4 @@
-# syntax=docker/dockerfile:1.18
+# syntax=docker/dockerfile:1.19
 FROM redhat/ubi9:9.6@sha256:dbc1e98d14a022542e45b5f22e0206d3f86b5bdf237b58ee7170c9ddd1b3a283 AS rpm-build
 RUN mkdir -p /rpms/ \
     && dnf install rpm-build gcc make cmake -y \

tests/Dockerfile

@@ -1,10 +1,4 @@
-# syntax=docker/dockerfile:1.18
-# this is here so we can grab the latest version of kind and have dependabot keep it up to date
-FROM kindest/node:v1.34.0@sha256:7416a61b42b1662ca6ca89f02028ac133a309a2a30ba309614e8ec94d976dc5a
-
-# this is here so we can grab the latest version of skopeo and have dependabot keep it up to date
-FROM quay.io/skopeo/stable:v1.20.0-immutable@sha256:519b95573a7490eb4740c8180d3dc33d86417222956e655719e74d3509586a33
-
+# syntax=docker/dockerfile:1.19
 FROM python:3.13-bookworm@sha256:c900d35aba5fe4c1dc1cd358408baae2902ff2a2926a1d15cc5002c6061ddb2e
 
 RUN apt-get update \