Support GHC 9.2 about doctest

[LeventErkok]

@andreasabel @RyanGlScott

Now that 9.2.1 is officially out, it'd be really nice to have this release. Here's what I'm seeing when trying to compile with 9.2.1:

[ 1 of 15] Compiling GhcUtil

src/GhcUtil.hs:100:7: error: Not in scope: ‘hscTarget’
    |
100 |       hscTarget = HscNothing
    |       ^^^^^^^^^

[RyanGlScott]

Just to clarify, I'm not a doctest maintainer. I often find myself writing patches for head.hackage, but there's no guarantee that the code in a head.hackage patch will correspond to the code you'd actually want to put in a new release. Among other reasons:

• head.hackage only needs to support the latest GHC release, so sometimes head.hackage patches won't compile on all GHC versions.
• I'm far from an expert on the libraries that I'm patching (doctest included), so some of the patches I write may deviate from the code style that a library's maintainers would prefer.