add deconflict-ctx test against regression (#3556)

test/runtime/samples/deconflict-ctx/_config.js

@@ -0,0 +1,5 @@
+export default {
+	html: `
+		<h1>Hello world!</h1>
+	`
+};

test/runtime/samples/deconflict-ctx/main.svelte

@@ -0,0 +1,5 @@
+<script>
+	const ctx = 'world';
+</script>
+
+<h1>Hello {ctx}!</h1>