Simplify git clone code in CI test (#1422)

1. Simplify git clone code in CI test. 
2. Replace git clone branch in Dockerfile.

Signed-off-by: chensuyue <suyue.chen@intel.com>

WorkflowExecAgent/tests/1_build_images.sh

@@ -9,7 +9,7 @@ echo "WORKDIR=${WORKDIR}"
 
 function get_genai_comps() {
     if [ ! -d "GenAIComps" ] ; then
-        git clone https://github.com/opea-project/GenAIComps.git && cd GenAIComps && git checkout "${opea_branch:-"main"}" && cd ../
+        git clone --depth 1 --branch ${opea_branch:-"main"} https://github.com/opea-project/GenAIComps.git
     fi
 }