Do not overwrite ret code in level_zero_shared_memory example

[vinser52]

Description

While working on the #1086 I found that the umf_example_level_zero_shared_memory returns success even the actual flow failed. See the output below:

test 1
    Start 1: umf_example_level_zero_shared_memory

1: Test command: /home/test-user/actions-runner/_work/unified-memory-framework/unified-memory-framework/build/examples-standalone/level_zero_shared_memory/umf_example_level_zero_shared_memory
1: Test timeout computed to be: 10000000
1: [FATAL UMF] utils_open_library: dlopen(libze_loader.so) failed with error: (null)
1: [FATAL UMF] ze_memory_provider_initialize: Loading Level Zero symbols failed
1: Failed to create a memory provider!
1/1 Test #1: umf_example_level_zero_shared_memory ...   Passed    0.06 sec

Checklist

• Code compiles without errors locally
• All tests pass locally
• CI workflows execute properly