ci: Try using older version of ghc-source-gen

[varungandhi-src]

There seems to be a build failure with ghc-source-gen-0.4.4.0 when
using GHC 8.10, so attempt to tell cabal to use an older version.

 src/GHC/SourceGen/Module.hs:191:41: error:
Error:     Variable not in scope: unqual :: OccNameStr -> RdrNameStr
    |
191 |                     (map (wrappedName . unqual) cs)
    |                                         ^^^^^^
Error: cabal: Failed to build ghc-source-gen-0.4.4.0 (which is required by
exe:proto-lens-protoc from proto-lens-protoc-0.7.1.1). See the build log above
for details.

Source: https://github.com/sourcegraph/scip/actions/runs/7322644181/job/19944384186?pr=226

Test plan

CI passes