fix: return type issue for php8.1

[saysource]

Without setting the return type in the exceptions, I get the error already logged here:

#369

Hope this helps, it is a really simple fix.

[webignition]

This is a subset of the changes in PR #366.

Perhaps this should be closed in preference to merging #366 as that also includes additional SF7 compatibility changes.

[saysource]

Yep, closing.