Fix building on Fedora 39 and Ubuntu 24.04 (#354)

### Motivation:

Fixes #278.

### Modifications:

Fixed tests to successfully compile on Fedora 39 and Ubuntu 24.04, which
they previously failed on.

### Result:

Ability to run tests on these two platforms again.

Add Scout to the list of available backends (#337)

* Add Scout to the list of available backends

* Update README.md

Disable existential any build setting (#312)

Motivation:

On 5.8, if the experiment existential any setting is enabled and a
consuming package holds an existential of a type from swift-log without
an explicit 'any' then the build will fail.

Modifications:

- Disable the setting

Result:

Users of 5.8 aren't broken

Update README.md add shipbook as backend (#304)

Motivation:

Added shipbook as backend for the library.

Modifications:

Just added it to the backend list.

Result:

Will have a fuller list.

1.4.3