Fix docker check warnings (#11474)

Dockerfile.local

 ARG GOLANG=golang:1.22.9-alpine3.19
-FROM ${GOLANG} as infra
+FROM ${GOLANG} AS infra
 
-ARG http_proxy=$http_proxy
-ARG https_proxy=$https_proxy
-ARG no_proxy=$no_proxy
+ARG http_proxy
+ARG https_proxy
+ARG no_proxy
 ENV http_proxy=$http_proxy
 ENV https_proxy=$https_proxy
 ENV no_proxy=$no_proxy
@@ -28,13 +28,13 @@ RUN if [ "$(go env GOARCH)" = "amd64" ]; then \
     fi
 
 ARG SELINUX=true
-ENV SELINUX $SELINUX
-ENV STATIC_BUILD true
+ENV SELINUX=$SELINUX
+ENV STATIC_BUILD=true
 ENV SRC_DIR=/go/src/github.com/k3s-io/k3s
 WORKDIR ${SRC_DIR}/
 
 
-FROM infra as build
+FROM infra AS build
 
 ARG SKIP_VALIDATE
 
@@ -60,7 +60,7 @@ RUN --mount=type=cache,id=gomod,target=/go/pkg/mod \
 
 RUN ./scripts/binary_size_check.sh
 
-FROM scratch as result
+FROM scratch AS result
 ENV SRC_DIR=/go/src/github.com/k3s-io/k3s
 COPY --from=build ${SRC_DIR}/dist /dist
 COPY --from=build ${SRC_DIR}/bin /bin

Dockerfile.test

 ARG GOLANG=golang:1.22.9-alpine3.20
-FROM ${GOLANG} as test-base
+FROM ${GOLANG} AS test-base
 
 RUN apk -U --no-cache add bash jq
-ENV K3S_SOURCE /go/src/github.com/k3s-io/k3s/
+ENV K3S_SOURCE=/go/src/github.com/k3s-io/k3s/
 WORKDIR ${K3S_SOURCE}
 
 COPY . ${K3S_SOURCE}
 
-FROM test-base as test-mods
+FROM test-base AS test-mods
 
 COPY ./scripts/test-mods /bin/
 ENTRYPOINT ["/bin/test-mods"]
 
-FROM test-base as test-k3s
+FROM test-base AS test-k3s
 
 RUN apk -U --no-cache add git gcc musl-dev docker curl coreutils python3 openssl py3-pip procps findutils yq pipx
 
 RUN PIPX_BIN_DIR=/usr/local/bin pipx install awscli
 
-ENV SONOBUOY_VERSION 0.57.2
+ENV SONOBUOY_VERSION=0.57.2
 
 RUN OS=linux; \
     ARCH=$(go env GOARCH); \
@@ -30,7 +30,7 @@ RUN OS=linux; \
     curl -fsL https://storage.googleapis.com/kubernetes-release/release/${RELEASE}/bin/linux/${ARCH}/kubectl -o /usr/local/bin/kubectl; \
     chmod a+x /usr/local/bin/kubectl; 
 
-ENV TEST_CLEANUP true
+ENV TEST_CLEANUP=true
 
 ENTRYPOINT ["./scripts/entry.sh"]
 CMD ["test"]