deps: Upgrade smarty/smarty to version 4.5.4

This eliminates a potential vulnerability where an template author could inject arbitrary PHP files to be run via the 'extends' tag.

See:

• https://github.com/smarty-php/smarty/security/advisories/GHSA-4rmg-292m-wg3w
• https://github.com/smarty-php/smarty/commit/0be92bc8a6fb83e6e0d883946f7e7c09ba4e857a

Impact assessment:

In our case I would consider this a low severity issue as we don't allow users to dynamically add or edit smarty templates. Templates has to be updated via merge requests, or by installing a theme. In both cases a malicious attacker already has easier ways to inject whatever code they want.

Further, the extend tag is not in use in any of our core templates.