CMake: Fix our c-ares version discovery

c-ares 1.34.0 and later generate ARES_VERSION_STR using a macro, so
fetch the version from ARES_VERSION_MAJOR, ARES_VERSION_MINOR, and
ARES_VERSION_PATCH.

Fixes #20125


(cherry picked from commit 7c141862)

Co-authored-by: Gerald Combs <gerald@wireshark.org>