Fixes #8368

```
>>> laplace_transform(cosh(t),t,s,noconds=True)
s/(s**2 - 1)
>>> laplace_transform(sinh(t),t,s,noconds=True)
1/(s**2 - 1)
```

Condition 30 in the _check_antecedents function mistakenly had the check s+t>0, when in fact the actual condition in Prudnikov is s+t>u. However, if you make that change then laplace transforms will fail for *both* sinh and cosh.

I got my hands on a copy of Prudnikov today and checked the two functions for cosh against his condition list. None of them were satisfied. I don't really know whether that means he had a typo or this is a case where Prudnikov's conditions just don't apply.

This PR compromises by using weak equality, the bare minimum of what we need for sinh and cosh to work. If we prefer to adhere to Prudnikov, the fix is to change these two inequalities to strict, which still modifies condition 24.