Implicitly marking parameter as nullable is deprecated

[oojacoboo]

So, PHP 8.4 deprecated implicit nullability.

    public function withFooQuery(
        callable $callable,
        string $relationAlias = null,  // Can't do this anymore
        ?string $joinType = Criteria::LEFT_JOIN
    )

Instead it must be:

    public function withFooQuery(
        callable $callable,
        ?string $relationAlias = null,
        ?string $joinType = Criteria::LEFT_JOIN
    )

I noticed this error on these methods, but it also occurs in the base classes in setters where the parameter is nullable (fixed by #37), and I'm sure in many others as well.

[oojacoboo]

See PR from Propel propelorm#2019

[mringler]

The things they just leave laying around...

Do you want to approve the merge at #40?

[oojacoboo]

@mringler Just an FYI, in the PR, if you add closes #38, it will automatically close the issue ticket when the PR is merged.