testsuite: fix T23540 fragility on 32-bit platforms

T23540 is fragile on 32-bit platforms. The root cause is usage of
`getEvidenceTreesAtPoint`, which internally relies on `Name`'s `Ord`
instance, which is indeterministic. The solution is adding a
deterministic `Ord` instance for `EvidenceInfo` and sorting the
evidence trees before pretty printing. Fixes #24449.