Bugfix/php8.4 and up imap removal

[bigcalm]

The IMAP extension has been removed from PHP from version 8.4.

Install candidates have since been removed from Debian unstable.

See: https://tracker.debian.org/news/1672837/removed-3103-1-from-unstable/

2nd commit - based upon PR #402 - installs the extension if the PHP version is lower than 8.4.

Fixes issue #444

[pfrenssen]

Thanks very much for working on this! I think the proposed solution certainly achieves the goal but is maybe not the best solution to facilitate future maintenance of the role.

If we now start managing version-specific extension overrides in main.yml tasks this will set us on a path towards a proliferation of similar tasks when more and more extension changes are introduced in new PHP versions.

In the role we handle overrides in the distro-specific vars files. I do agree that this is not the best possible solution (after all, the IMAP extension removal is specific to PHP 8.4, not necessarily to a certain version of a distro), but it will make it more easily manageable. It also points users to the fact they can take control of the variables for their own machines.

[bigcalm]

It's been a while since I worked on this, but I think I was mirroring how the role catered for when JSON was absorbed into the core of PHP.

Happy to see the role working with Ubuntu 26.04 with your PR instead.