ci: a suite named chainsaw-test.yml is invisible to select-e2e and select-install #4205

Two scripts enumerate Chainsaw suites by an exact filename, so a suite written as chainsaw-test.yml is invisible to both:

hack/select-e2e.sh:171      find hack/e2e-chainsaw -mindepth 2 -maxdepth 2 -name chainsaw-test.yaml
hack/select-install.sh:106  find "$1" -mindepth 2 -maxdepth 2 -name chainsaw-test.yaml 2>/dev/null

The tree is uniformly .yaml today, so nothing is broken right now. What makes it worth a ticket is the direction each one fails in. A suite that is not listed does not red anything: select-e2e prints a selection that silently lacks it, and the suite never runs. .yml is a live spelling elsewhere in this repo (.github/*.yml, the multus manifests), so a contributor writing it is following a pattern the tree already shows them.

select-e2e.sh at least refuses when find itself fails, and says so in the comment above that line. select-install.sh sends the same call's errors to /dev/null, so there a failed find and an empty directory read the same, which is the second half of the problem in that file. #3669 covers the pipe-status defects in the same script and not this.

Accepting both spellings is one \( -name chainsaw-test.yaml -o -name chainsaw-test.yml \) in each place. Rejecting the second spelling outright would also close it, as long as the rejection is loud: what cannot stay is a suite that exists and is never selected.