[flake] downgrade haskell.nix according to julm's remarks

nix flake lock --override-input haskell-nix github:input-output-hk/haskell.nix/a921f7340c0c1a561f0e743d4b07b8130ea5c5be

flake.lock

@@ -543,11 +543,11 @@
         "stackage": "stackage"
       },
       "locked": {
-        "lastModified": 1728348642,
-        "narHash": "sha256-NUngjkPKengqaFoq9yg3ODzNhN3dql9M2HV0cX3Ek/8=",
+        "lastModified": 1726534207,
+        "narHash": "sha256-yP7jf1wFfAObRNkKM6xomzbFcuJ/LGaUZE0YZ2l0DR4=",
         "owner": "input-output-hk",
         "repo": "haskell.nix",
-        "rev": "507194171ca6f4ca58e9e026c115211f08e1bf45",
+        "rev": "a921f7340c0c1a561f0e743d4b07b8130ea5c5be",
         "type": "github"
       },
       "original": {
@@ -743,16 +743,16 @@
     "hls-2.9": {
       "flake": false,
       "locked": {
-        "lastModified": 1720003792,
-        "narHash": "sha256-qnDx8Pk0UxtoPr7BimEsAZh9g2WuTuMB/kGqnmdryKs=",
+        "lastModified": 1718469202,
+        "narHash": "sha256-THXSz+iwB1yQQsr/PY151+2GvtoJnTIB2pIQ4OzfjD4=",
         "owner": "haskell",
         "repo": "haskell-language-server",
-        "rev": "0c1817cb2babef0765e4e72dd297c013e8e3d12b",
+        "rev": "40891bccb235ebacce020b598b083eab9dda80f1",
         "type": "github"
       },
       "original": {
         "owner": "haskell",
-        "ref": "2.9.0.1",
+        "ref": "2.9.0.0",
         "repo": "haskell-language-server",
         "type": "github"
       }