The command string syntax is preventing the --skip-kext-approval-check switch from being read.
Format the command string with single quotes surrounding the installer path and the company code to ensure the switch is read.
Example:
sudo /tmp/cbdefense_install_unattended.sh -i ‘/tmp/CbDefense Install.pkg’ -c ‘ExampleCompanyCode’ --skip-kext-approval-check
ALLOW_INSTALL_UPGRADE_WITHOUT_KEXT_PREAPPROVAL=1