Update for GHC2024 language extension edition

Author: mpilgrem

CONTRIBUTING.md

@@ -416,9 +416,21 @@ stack exec -- sh ./etc/scripts/hlint.sh
 
 ## Code syntax
 
-Stack makes use of GHC's `GHC2021` collection of language extensions, which is
+Stack makes use of GHC's `GHC2024` collection of language extensions. That is
 set using the `language` key in the `package.yaml` file.
 
+The `GHC2024` edition enables the `MonoLocalBinds` language extension. Enabling
+the extension can change how GHC infers the types of local bindings (that is,
+let-bound or where-bound variables). When enabled it means that the types of a
+group of local bindings are not generalised unless:
+
+* any of its binders has a partial type signature; or
+
+* all of its free variables are closed. If a variable is closed then its type
+  definitely has no free type variables. A variable imported from another module
+  is closed. A variable that is let-bound and has an explicit type signature
+  with no free type variables is closed.
+
 Stack makes use of single-constructor types where the constructor has a large
 number of fields. Some of those fields have similar types, and so on. Given
 that, Stack makes use of `OverloadedRecordDot`, introduced in GHC 9.2.1. It also
@@ -510,8 +522,8 @@ stack test
 
 The `--file-watch` is a very useful option to get quick feedback. However,
 running the entire test suite after each file change will slow you down. You
-will need to specify which test suite (unit test or integration) and pass 
-arguments to specify which module you'd specifically like to run to get quick 
+will need to specify which test suite (unit test or integration) and pass
+arguments to specify which module you'd specifically like to run to get quick
 feedback. A description of this follows below.