Quite a few vectoriser tests were using a trip count of 1024,
- For fixed-length VFs we would never actually tail-fold, e.g. see Transforms/LoopVectorize/RISCV/uniform-load-store.ll. This is because we can prove at compile-time there will never be a scalar tail.
- As of D146199 the same optimisation mentioned above will also apply to scalable VFs too.
I've changed all such trip counts to be 1025 instead.