Fix union typo

The "set clipboard" event used the wrong union type to store its text.

In practice, it worked because both are at the same offset.

app/src/control_msg.c

@@ -67,7 +67,7 @@ control_msg_serialize(const struct control_msg *msg, unsigned char *buf) {
                              (uint32_t) msg->inject_scroll_event.vscroll);
             return 21;
         case CONTROL_MSG_TYPE_SET_CLIPBOARD: {
-            size_t len = write_string(msg->inject_text.text,
+            size_t len = write_string(msg->set_clipboard.text,
                                       CONTROL_MSG_CLIPBOARD_TEXT_MAX_LENGTH,
                                       &buf[1]);
             return 1 + len;

app/tests/test_control_msg_serialize.c

@@ -200,7 +200,7 @@ static void test_serialize_get_clipboard(void) {
 static void test_serialize_set_clipboard(void) {
     struct control_msg msg = {
         .type = CONTROL_MSG_TYPE_SET_CLIPBOARD,
-        .inject_text = {
+        .set_clipboard = {
             .text = "hello, world!",
         },
     };