test(checkbox): test multiple checkbox reactivity for same object

Regression tests for #2177

tests/Checkbox/MultipleCheckboxesObject.test.svelte

@@ -0,0 +1,15 @@
+<script lang="ts">
+  import { Checkbox } from "carbon-components-svelte";
+
+  export let obj = {
+    a: false,
+    b: false,
+  };
+
+  $: console.log("object changed:", obj);
+</script>
+
+<Checkbox bind:checked={obj.a} labelText="A" data-testid="checkbox-a" />
+<Checkbox bind:checked={obj.b} labelText="B" data-testid="checkbox-b" />
+
+<span data-testid="object-values">{JSON.stringify(obj)}</span>