[openmage/magento-lts] Fix for authenticated remote code execution through layout update

Impact

A layout block was able to bypass the block blacklist to execute remote code.

References

• https://github.com/OpenMage/magento-lts/security/advisories/GHSA-5j2g-3ph4-rgvm
• https://github.com/OpenMage/magento-lts/releases/tag/v19.4.22
• https://github.com/OpenMage/magento-lts/releases/tag/v20.0.19
• https://nvd.nist.gov/vuln/detail/CVE-2021-41144
• https://github.com/OpenMage/magento-lts/commit/06c45940ba3256cdfc9feea12a3c0ca56d23acf8
• https://github.com/advisories/GHSA-5j2g-3ph4-rgvm