[cmake] Fix warnings.

cmake spits the following warning on newer versions. Details can be found here http://www.cmake.org/Bug/view.php?id=14441

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    CMake Warning (dev) at tests/src/python/CMakeLists.txt:1 (INCLUDE):
      Syntax Warning in cmake code at
    
        /home/kk/dev/cpp/qgis/QGIS/cmake/UsePythonTest.cmake:60:12
    
      Argument not separated from preceding token by whitespace.
    This warning is for project developers.  Use -Wno-dev to suppress it.
    
    CMake Warning (dev) at tests/src/python/CMakeLists.txt:1 (INCLUDE):
      Syntax Warning in cmake code at
    
        /home/kk/dev/cpp/qgis/QGIS/cmake/UsePythonTest.cmake:60:29
    
      Argument not separated from preceding token by whitespace.
    This warning is for project developers.  Use -Wno-dev to suppress it.
    
    CMake Warning (dev) at tests/src/python/CMakeLists.txt:1 (INCLUDE):
      Syntax Warning in cmake code at
    
        /home/kk/dev/cpp/qgis/QGIS/cmake/UsePythonTest.cmake:63:23
    
      Argument not separated from preceding token by whitespace.
    This warning is for project developers.  Use -Wno-dev to suppress it.
    
    CMake Warning (dev) at tests/src/python/CMakeLists.txt:1 (INCLUDE):
      Syntax Warning in cmake code at
    
        /home/kk/dev/cpp/qgis/QGIS/cmake/UsePythonTest.cmake:63:37
    
      Argument not separated from preceding token by whitespace.
    This warning is for project developers.  Use -Wno-dev to suppress it.