ci: Try using older version of ghc-source-gen (#228)

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

Author: varungandhi-src

.github/workflows/protobuf.yml

@@ -9,6 +9,7 @@ on:
       - 'scip.proto'
       - 'buf**'
       - '.tool-versions'
+      - 'dev/proto-generate.sh'
 
 jobs:
   protoc-gen-up-to-date:

dev/proto-generate.sh

@@ -19,7 +19,7 @@ fi
 
 echo "--- Haskell ---"
 command -v cabal > /dev/null 2>&1 || { echo >&2 "Haskell's 'cabal' command is not installed. Please install it first via https://www.haskell.org/ghcup/"; exit 1; }
-cabal install proto-lens-protoc-0.7.1.1 --overwrite-policy=always --ghc-options='-j2 +RTS -A32m'
+cabal install proto-lens-protoc-0.7.1.1 ghc-source-gen-0.4.3.0 --overwrite-policy=always --ghc-options='-j2 +RTS -A32m'
 ln -sfv `which proto-lens-protoc` "$PWD/.bin/protoc-gen-haskell"
 PATH="$PWD/.bin:$PATH"