selftests/bpf: check if imprecise stack spills confuse infinite loop detection

Verify that infinite loop detection logic separates states with
identical register states but different imprecise scalars spilled to
stack.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20240108205209.838365-4-maxtram95@gmail.com


Signed-off-by: Alexei Starovoitov <ast@kernel.org>