test: skip the 2D_hybrid_slab example golden (not portable across compilers)

The diffusion flame over the fuel slab is positioned by accumulated stiff-kinetics roundoff, so by step 50 the transverse momentum drifts past the 1e-3 Example tolerance: nvhpc lanes pass, Intel and Frontier CCE disagree with the golden by ~2e-3 absolute (up to 44% relative on a small component). Same non-portability class as 1D_propellant_flame and the other flame examples already skipped there, so no single golden passes every lane. The case remains a runnable example; the reactive_burn, shock_flame, ibm_burning_grain and ibm_flameholder goldens are unaffected and pass on all lanes.

Author: sbryngelson