Update slang-rhi

[skallweitNV]

slang-rhi needs to be updated to latest. There are tests failing in ToT slang-rhi with latest slang release, so updating slang-rhi submodule should allow seeing those breakages in slang.

[aasgaonkar]

we already have slang-rhi testing enabled for slang CI, which uses the slang-rhi built from slang checkout/builds. This should be updating the submodule to pick latest, right?

[skallweitNV]

Yes, #7303 is doing that.