Remove WITH_GUI_TESTS exclusion for CLI tests (#6946)

Apparently this exclusion was only relevant for Linux
systems not running X, which was already handled dynamically
in the testClip function. The CLI tests will now run by default
will all the other core tests.

tests/CMakeLists.txt

@@ -236,11 +236,9 @@ if(WITH_XC_BROWSER)
         LIBS ${TEST_LIBRARIES})
 endif()
 
+add_unit_test(NAME testcli SOURCES TestCli.cpp
+        LIBS testsupport cli ${TEST_LIBRARIES})
 
 if(WITH_GUI_TESTS)
-    # CLI clip tests need X environment on Linux
-    add_unit_test(NAME testcli SOURCES TestCli.cpp
-            LIBS testsupport cli ${TEST_LIBRARIES})
-
     add_subdirectory(gui)
 endif(WITH_GUI_TESTS)