Upgrade Verilator dependency

[nasahlpa]

As discussed with @rswarbrick in PR #2129, it might be worth to upgrade the Verilator dependency. That reason is that we got some linting errors, i.e., IMPERFECTSCH, that were removed in more recent Verilator versions.

When upgrading Verilator, it might also be worth to get rid of the following hack to get rid of the linting error:

ibex/rtl/ibex_lockstep.sv

Line 139 in 2f040eb

assign rst_shadow_set_single_bit = rst_shadow_set_q[0];