Fix dockerfile linter warnings (#2291)

core/iwasm/libraries/wasi-nn/test/Dockerfile.cpu

@@ -5,8 +5,9 @@ FROM ubuntu:20.04 AS base
 
 ENV DEBIAN_FRONTEND=noninteractive
 
+# hadolint ignore=DL3008
 RUN apt-get update && apt-get install -y \
-    cmake build-essential git
+  cmake build-essential git --no-install-recommends
 
 WORKDIR /home/wamr
 
@@ -14,11 +15,18 @@ COPY . .
 
 WORKDIR /home/wamr/core/iwasm/libraries/wasi-nn/test/build
 
+# hadolint ignore=DL3008
+RUN apt-get install -y wget ca-certificates --no-install-recommends \
+  && mkdir /usr/local/share/ca-certificates/cacert.org \
+  && wget -qP /usr/local/share/ca-certificates/cacert.org http://www.cacert.org/certs/root.crt http://www.cacert.org/certs/class3.crt \
+  && update-ca-certificates \
+  && git config --global http.sslCAinfo /etc/ssl/certs/ca-certificates.crt
+
 RUN cmake \
   -DWAMR_BUILD_WASI_NN=1 \
   ..
 
-RUN make -j $(grep -c ^processor /proc/cpuinfo)
+RUN make -j "$(grep -c ^processor /proc/cpuinfo)"
 
 FROM ubuntu:22.04