highlighter: Add a test case for Rust nested vec macros

fixtures/highlighter/nested_vec.rs

@@ -0,0 +1,5 @@
+   vec![vec![]]
+// ┡━━┛╿┡━━┛┗━┹─ punctuation.bracket
+// │   │╰─ function.macro
+// │   ╰─ punctuation.bracket
+// ╰─ function.macro

fixtures/injections/nested_vec.rs

@@ -0,0 +1,4 @@
+   vec![vec![]]
+//     ┡━━━┛┡┛╰─ rust
+//     │    ╰─ rust rust
+//     ╰─ rust

highlighter/src/tests.rs

@@ -446,6 +446,13 @@ fn injection_precedence() {
     injection_fixture(&loader, "injections/overlapping_injection.rs");
 }
 
+#[test]
+fn rust_nested_vec() {
+    let loader = TestLanguageLoader::new();
+    highlight_fixture(&loader, "highlighter/nested_vec.rs");
+    injection_fixture(&loader, "injections/nested_vec.rs");
+}
+
 #[test]
 fn edit_remove_and_add_injection_layer() {
     let loader = TestLanguageLoader::new();