shogun: disable tests that take too long

The checkPhase may take from 30 minutes up to 2 hours and 30 minutes on
Hydra due to these tests:

[...]
311/375 Test #311: libshogun-evaluation_cross_validation_classification ............ Passed 247.33 sec
312/375 Test #313: libshogun-evaluation_cross_validation_mkl_weight_storage ........ Passed 428.31 sec
315/375 Test #312: libshogun-evaluation_cross_validation_locked_comparison ......... Passed 880.44 sec
341/375 Test #316: libshogun-evaluation_cross_validation_regression ................ Passed 380.48 sec
342/375 Test #343: libshogun-modelselection_grid_search_kernel ..................... Passed 4866.85 sec
343/375 Test #344: libshogun-modelselection_grid_search_linear ..................... Passed 574.78 sec
345/375 Test #342: libshogun-modelselection_combined_kernel_sub_parameters ......... Passed 5929.90 sec
375/375 Test #346: libshogun-modelselection_grid_search_multiclass_svm ............. Passed 1826.27 sec
[...]
Total Test time (real) = 9046.65 sec
checkPhase completed in 2 hours 30 minutes 47 seconds

pkgs/applications/science/machine-learning/shogun/default.nix

···
     excludeTestsRegex = lib.concatStringsSep "|" [
       # sporadic segfault
       "TrainedModelSerialization"
+      # these take too long on CI
+      "evaluation_cross_validation"
+      "modelselection_combined_kernel"
+      "modelselection_grid_search"
     ];
   in [
     "-DBUILD_META_EXAMPLES=ON"