Corpus ratchet red on master: Pool and Tree gained a second definition #7315

The types ratchet in Corpus Ratchet fails on master since 26c4c63 (#7270) and 0a05923 (#7216): tri types ratchet reports ledger 84 names, observed 86, with NEW conflicts Pool (specs/tri/t27b/conformance/scope_exit.t27) and Tree (specs/tri/t27b/conformance/unresolved_signature.t27). Both are small t27b conformance fixtures whose struct name collides with an existing type elsewhere in the corpus.

Fix: give the two fixture structs unique names (ExitPool, KidTree) instead of blessing two new conflicts into the ledger. Behaviour of both fixtures is unchanged.

Every open PR currently inherits this red (e.g. #7295, #7150).