fix: account for mustache inside mustache (#1091)

Author: ottomated

.changeset/better-rice-join.md

@@ -0,0 +1,5 @@
+---
+'eslint-plugin-svelte': patch
+---
+
+fix: Don't remove mustache'd string literals if they contain curly braces

packages/eslint-plugin-svelte/src/rules/no-useless-mustaches.ts

@@ -85,6 +85,10 @@ export default createRule('no-useless-mustaches', {
 				return;
 			}
 
+			if (rawValue.includes('{')) {
+				return;
+			}
+
 			let hasEscape = false;
 			if (rawValue !== strValue) {
 				// check escapes

packages/eslint-plugin-svelte/tests/fixtures/rules/no-useless-mustaches/valid/valid-test01-input.svelte

@@ -8,5 +8,6 @@ foo 'foo'
 {1}
 {null}
 {`foo${foo}`}
+{'{foo'}
 
 <div data-text="foo 'foo' {foo} {'foo' || 'bar'} {1} {null}" />