Use GHC 9.6 compatible ghc-source-gen

Author: avdv

stackage_snapshot_9.6.2.yaml

@@ -5,6 +5,6 @@ packages:
 - git: https://github.com/avdv/proto-lens
   commit: 2ab0a8d1ec1f54f3d1a0ecd1a257311389126490
 
-# support GHC 9.4 (see https://github.com/google/ghc-source-gen/pull/102)
-- git: https://github.com/circuithub/ghc-source-gen
-  commit: 7a6aac047b706508e85ba2054b5bedbecfd7eb7a
+# support GHC 9.6
+- git: https://github.com/avdv/ghc-source-gen
+  commit: 4bc81b85c21094d1dc38b86205b1725b379a6e83