[tests] use a valid hexadecimal string instead of a placeholder

[faaany]

Summary

In the latest code of get_cache_manager of the triton library (https://github.com/triton-lang/triton/blob/1bb8b8055c81f6bb85055645a20e0dbd27d5295f/python/triton/runtime/cache.py#L261), the key needs to be a valid hexadecimal string, otherwise the test will fail.

This PR fixes the issue by using a valid hex string instead of a placeholder.

Testing Done

The test passes both on CUDA and XPU.

========================================================== PASSES ===========================================================
================================================== short test summary info ==================================================
PASSED test/triton/test_triton_monkey_patch.py::test_import_custom_cache_manager
=============================================== 1 passed, 1 warning in 0.12s ================================================

On Intel(R) Data Center GPU Max 1550 and NV GPU A100

• Hardware Type:
• run make test to ensure correctness
• run make checkstyle to ensure code style
• run make test-convergence to ensure convergence

[faaany]

@sywangyi @yao-matrix