[HIP][test] Avoid %T

[HIP][test] Avoid %T

%T is a deprecated lit feature. It refers to the parent directory.
When two tests in test/Driver refer to the same `%T/foo`, they are racy with each other.
%t includes the test name and is safe for use.

Reviewed By: tra

Differential Revision: https://reviews.llvm.org/D133998