clang-cuda-l4, clang-cuda-p4, and clang-cuda-t4 are not reliable

[gkistanova]

Here is the example of false negatives (when failure does not seem related to the commit a builder builds) from these 3 builders:

• https://github.com/llvm/llvm-project/pull/68846#issuecomment-2186028673,
• https://github.com/llvm/llvm-project/pull/68846#issuecomment-2186034080,
• https://github.com/llvm/llvm-project/pull/68846#issuecomment-2186035287.

For the mean time I marked them silent (no failure reporting to blame lists or github).

[fhahn]

Thanks!