fix: CVE-2025-61729 - update contrib Dockerfile to use Go 1.25.6

Signed-off-by: Shubham Bhardwaj <shubbhar@redhat.com>

Author: infernus01

contrib/tkn-image/Dockerfile

@@ -1,11 +1,11 @@
-ARG GOLANG_VERSION=1.17.13
-ARG DEBIAN_VERSION=10
+ARG GOLANG_VERSION=1.25.6
+ARG DEBIAN_VERSION=12
 
-FROM golang:${GOLANG_VERSION} as builder
+FROM golang:${GOLANG_VERSION} AS builder
 ARG RELEASE_VERSION=
 COPY . /go/src/github.com/tektoncd/cli
 WORKDIR /go/src/github.com/tektoncd/cli
 RUN make RELEASE_VERSION=${RELEASE_VERSION} bin/tkn
 
-FROM debian:${DEBIAN_VERSION} as tkn
+FROM debian:${DEBIAN_VERSION} AS tkn
 COPY --from=builder /go/src/github.com/tektoncd/cli/bin/tkn /usr/bin