Add dev images for php-8.4 development
Support developers to use php-8.4, since we are also running that version in CI and plan to move away from php8.3 in the long term.
Bug: T419004
How to register an account on GitLab. Due to spam, new accounts are locked until approved by an admin or the approver bot. Your GitLab account gets automatically approved within one hour if you are a member of Trusted Contributors in Gerrit, or a member of the Trusted-Contributors group in Phabricator and linked your Developer account ("LDAP") to your Phabricator account. If none of these apply, file an unlock request to expedite access. Only if you are WMF staff: Create your GitLab account, have "Wmf" group membership in IDM, link your Developer account ("LDAP") to your Phabricator account, and get automatically approved.
Support: mw:GitLab, how to host a project on GitLab, #wikimedia-gitlab on libera.chat, #GitLab on Phabricator.
Support developers to use php-8.4, since we are also running that version in CI and plan to move away from php8.3 in the long term.
Bug: T419004