googletest

cmake: find python in order specified by PATH environment variable.

CMake policy CMP0094 controls a lookup strategy used to find a Python
executable:

* CMP0094=OLD selects a Python executable with a higher version.
* CMP0094=NEW selects a Python executable found earlier in PATH.

NEW behavior is critical in presence of a Python virtual environment
established and activated, i.e. added to the PATH variable.

In case GoogleTest is embedded into a larger project, the result of
`find_package(Python)` affects the whole build, not only GoogleTest
component itself.