Fix (unreported) memleak in some BKE tests in multi-binaries case.

Some tests would access system paths somehow, which implicitely creates
the static `m_systemPaths` variable, but would not explicitely call
`GHOST_DisposeSystemPaths` at the end to release it.

Noticeable when disabling the `WITH_TESTS_SINGLE_BINARY` option.

source/blender/blenkernel/intern/image_partial_update_test.cc

@@ -5,6 +5,8 @@
 
 #include "CLG_log.h"
 
+#include "GHOST_Path-api.hh"
+
 #include "BKE_appdir.hh"
 #include "BKE_global.hh"
 #include "BKE_idtype.hh"
@@ -80,6 +82,7 @@ class ImagePartialUpdateTest : public testing::Test {
 
     IMB_moviecache_destruct();
     IMB_exit();
+    GHOST_DisposeSystemPaths();
     BKE_appdir_exit();
     CLG_exit();
   }

source/blender/blenkernel/intern/lib_query_test.cc

@@ -7,6 +7,8 @@
 
 #include "CLG_log.h"
 
+#include "GHOST_Path-api.hh"
+
 #include "DNA_constraint_types.h"
 #include "DNA_mesh_types.h"
 #include "DNA_node_types.h"
@@ -140,6 +142,7 @@ template<typename TestData> class Context {
     bke::BKE_node_system_exit();
     RNA_exit();
     IMB_exit();
+    GHOST_DisposeSystemPaths();
     BKE_appdir_exit();
     CLG_exit();
   }

source/blender/blenkernel/intern/lib_remap_test.cc

@@ -7,6 +7,8 @@
 
 #include "CLG_log.h"
 
+#include "GHOST_Path-api.hh"
+
 #include "DNA_mesh_types.h"
 #include "DNA_node_types.h"
 #include "DNA_object_types.h"
@@ -149,6 +151,7 @@ template<typename TestData> class Context {
     RNA_exit();
     IMB_exit();
     BKE_appdir_exit();
+    GHOST_DisposeSystemPaths();
     CLG_exit();
   }
 };