Add rustfmt test from #117942

Author: frank-king

src/tools/rustfmt/tests/target/anonymous-types.rs

@@ -16,4 +16,16 @@ struct Foo {
     e: f32,
 }
 
+// Test for issue 117942
+struct Foo {
+    _: union  {
+        #[rustfmt::skip]
+    f: String,
+    },
+    #[rustfmt::skip]
+    _: struct {
+    g: i32,
+    },
+}
+
 fn main() {}