CI: Install clang in the ci environments

To test PR kata-containers/kata-containers#8484, the compilation process for the kata-agent relies on clang.
The unit tests failed on arm64:
    http://jenkins.katacontainers.io/job/kata-containers-2.0-ubuntu20.04-ARM-unit/3419/consoleFull

Fixes: #5813

Signed-off-by: ChengyuZhu6 <chengyu.zhu@intel.com>

.ci/jenkins_job_build.sh

@@ -229,6 +229,8 @@ run_unit_test() {
 		pushd "${GOPATH}/src/${katacontainers_repo}"
 		echo "Installing yq"
 		sudo -E INSTALL_IN_GOPATH=false ./ci/install_yq.sh
+		echo "Install clang"
+		sudo -E apt-get install -y clang
 		echo "Installing libseccomp library from sources"
 		libseccomp_install_dir=$(mktemp -d -t libseccomp.XXXXXXXXXX)
 		gperf_install_dir=$(mktemp -d -t gperf.XXXXXXXXXX)