Lock PHP to 7.2
As 7.3 is not working with phpcs-security-audit: https://gitlab.com/gitlab-org/security-products/analyzers/phpcs-security-audit/-/jobs/158103558
As 7.3 is not working with phpcs-security-audit: https://gitlab.com/gitlab-org/security-products/analyzers/phpcs-security-audit/-/jobs/158103558