Map postgres :restrict_violation to :foreign_key constraint (#713)

In PostgreSQL 18, this error code is now used for `ON DELETE RESTRICT`
constraint violation. The existing `:foreign_key_violation` error code
is raised for `ON DELETE NO ACTION`.

The behaviour changed in postgres commit
postgres/postgres@086c84b

The change is backwards compatible as the error code was not previously
raised even though it existed in the postgres documentation. It is now
correctly raised for the `ON DELETE RESTRICT` constraint.

Author: ashutoshrishi

lib/ecto/adapters/postgres/connection.ex

@@ -28,6 +28,12 @@ if Code.ensure_loaded?(Postgrex) do
         ),
         do: [foreign_key: constraint]
 
+    def to_constraints(
+          %Postgrex.Error{postgres: %{code: :restrict_violation, constraint: constraint}},
+          _opts
+        ),
+        do: [foreign_key: constraint]
+
     def to_constraints(
           %Postgrex.Error{postgres: %{code: :exclusion_violation, constraint: constraint}},
           _opts