FindRuby: update to support versions up to 3.1 and fix a binary scanning bug

This PR updates the FindRuby module to support newer versions, up to 3.1.

Additionally it fixes a binary scanning bug, as described here:

The possible executable names list always starts with a plain ruby binary, which is scanned for first. If that does exist (which satisfies find_program), but doesn't match the requested version, the executable will be dismissed by _RUBY_VALIDATE_INTERPRETER (which is sane), but searching also stops.

Fix that by keeping the search going, removing items from the list as we go, until find_program returns a path that _RUBY_VALIDATE_INTERPRETER is happy with or the list is empty.