`find_package` searches prefixes specified by `<PackageName>_ROOT` environment and CMake variables since policy [CMP0074](https://cmake.org/cmake/help/v3.26/policy/CMP0074.html) was introduced by CMake 3.12 via !1858. The spelling of the `<PackageName>_ROOT` name preserves the exact case specified as the first argument to `find_package`. Discussion in https://gitlab.kitware.com/cmake/cmake/-/issues/24378#note_1315661 suggests that we should also check the upper-case name `<PACKAGENAME>_ROOT` because upper-case environment variable names are a common convention. Adding this will need a policy for compatibility. Some care will also be needed to deal with platforms that have case-insensitive environment variable lookup.