Add useConstraint modifier to the creation of the unique index.

Knex documentation says for the unique() function, that useConstraint will use a unique constraint and is default true for postgres when there is no predicate defined.
Issue #3200 specifies that we want a unique index.
Documentation can be found here: https://knexjs.org/guide/schema-builder.html#unique

packages/server/migrations/20240622205204_add-grant-notes-table.js

@@ -13,7 +13,10 @@ exports.up = function (knex) {
             table.foreign('grant_id').references('grants.grant_id');
             table.foreign('user_id').references('users.id');
 
-            table.unique(['grant_id', 'user_id'], 'idx_grant_id_user_id');
+            table.unique(['grant_id', 'user_id'], {
+                indexName: 'idx_grant_id_user_id',
+                useConstraint: false,
+              });
         })
         .createTable('grant_notes_revisions', (table) => {
             table.increments('id').notNullable().primary();