Does not configure when BUILD_TESTING=OFF

[Hugobros3]

CMake Error at external/abseil-cpp/CMake/AbseilHelpers.cmake:317 (target_link_libraries):
  The link interface of target "test_allocator" contains:

    GTest::gmock

  but the target was not found.  Possible reasons include:

    * There is a typo in the target name.
    * A find_package call is missing for an IMPORTED target.
    * An ALIAS target is missing.

Call Stack (most recent call first):
  external/abseil-cpp/absl/container/CMakeLists.txt:206 (absl_cc_library)

[m-kurtenacker]

Is ABSL_BUILD_TESTING set to ON by any chance?

[Hugobros3]

Nope