Avoid using $? directly in the if statement.

Fix ShellCheck SC2181 error

Ref: https://www.shellcheck.net/wiki/SC2181

Signed-off-by: Pradipta Banerjee <pradipta.banerjee@gmail.com>

config/peerpods/podvm/lib.sh

@@ -209,7 +209,8 @@ function prepare_source_code() {
     if [[ "${AGENT_POLICY}" ]]; then
         echo "Custom agent policy is being set through the AGENT_POLICY value"
         echo "${AGENT_POLICY}" | base64 -d >"${podvm_dir}"/files/etc/kata-opa/custom.rego
-        if [[ $? == 0 ]] && grep -q "agent_policy" "${podvm_dir}"/files/etc/kata-opa/custom.rego; then # checks policy validity
+        return_code=$?
+        if [[ "$return_code" == 0 ]] && grep -q "agent_policy" "${podvm_dir}"/files/etc/kata-opa/custom.rego; then # checks policy validity
             ln -sf custom.rego "${podvm_dir}"/files/etc/kata-opa/default-policy.rego
         else
             error_exit "Invalid AGENT_POLICY value set, expected base64 encoded valid agent policy, got: \"${AGENT_POLICY}\""