Add cabal-add source repository

We need to depend on a newer commit of cabal-add since the newest
release does not yet allow us to add modules to a cabal-file.

Once there is a new release of cabal-add we can revert this commit.

Author: VeryMilkyJoe

cabal.project

@@ -6,8 +6,11 @@ packages:
          ./ghcide
          ./hls-plugin-api
          ./hls-test-utils
-         ../cabal-add
 
+source-repository-package
+  type:     git
+  location: https://github.com/Bodigrim/cabal-add.git
+  tag:      83de92dcce6221d66bdedca0b462fedd3b06afce
 
 index-state: 2025-05-12T13:26:29Z