package/gli: disable tests

package/gli: disable tests

Disable tests to avoid the following build failure with gcc 11:

/srv/storage/autobuild/run/instance-2/output-1/build/gli-559cbe1ec38878e182507d331e0780fbae5baf15/test/core/core_convert.cpp: In function 'bool convert_rgb32f_rgb9e5(const char*, const char*)':
/srv/storage/autobuild/run/instance-2/output-1/build/gli-559cbe1ec38878e182507d331e0780fbae5baf15/test/core/core_convert.cpp:36:45: error: ordered comparison of pointer with integer zero ('const char*' and 'int')
   36 |         if(std::strstr(FilenameDst, ".dds") > 0 || std::strstr(FilenameDst, ".ktx") > 0)
      |            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~

Fixes:
 - http://autobuild.buildroot.org/results/4f1dbb7cf2b071f3b92d00d13984068ef5f5b329

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>