configure should not look for googletest when no tests are built

[yurivict]

Describe the bug
configure looks for googletest in the process of regular build:

-- Found GTest: /usr/local/lib/cmake/GTest/GTestConfig.cmake (found version "1.13.0")

Context
Version: 0.9.0

[thorstenhater]

Hi @yurivict,

I am not sure we can 'fix' this. Configure/CMake doesn't know -- and can never know -- that we are not building
tests or any related targets; that is done by the build step. Additionally, one configure step might serve to
build different targets: tests, examples, ... and all of might require different subsets of the full set of
dependencies.

Would you agree? If so, we can close this.

[thorstenhater]

Since we had no further feedback, I'll close this.

[yurivict]

@thorstenhater

Sorry, I missed your message.

cmake has the BUILD_TESTING variable, see here.

Test dependencies, including googletest, should be searched only when this variable is set.

[bcumming]

@yurivict , Arbor doesn't use CTest to build or run it's tests.

[yurivict]

@bcumming
BUILD_TESTING has nothing to do with ctest.