Disable failing loader and python compilation tests on macOS (#12497)

The failing tests are tracked by https://github.com/openxla/iree/issues/12496.
diff --git a/build_tools/cmake/ctest_all.sh b/build_tools/cmake/ctest_all.sh
index d093107..2837a2f 100755
--- a/build_tools/cmake/ctest_all.sh
+++ b/build_tools/cmake/ctest_all.sh
@@ -90,6 +90,13 @@
     # TODO(#11080): Fix arrays not matching in test_variant_list_buffers
     "iree/runtime/bindings/python/vm_types_test"
   )
+elif [[ "$OSTYPE" =~ ^darwin ]]; then
+  excluded_tests+=(
+    #TODO(#12496): Remove after fixing the test on macOS
+    "iree/compiler/bindings/c/loader_test"
+    #TODO(#12496): Remove after fixing the test on macOS
+    "iree/compiler/API/python/test/transforms/ireec/compile_sample_module"
+  )
 fi
 
 # TODO(#12305): figure out how to run samples with custom binary outputs