[lang2/macro] add failure UI test for #[ink(event)] provided with another #[ink(storage)]

lang2/macro/tests/compile_tests.rs

@@ -41,4 +41,5 @@ fn compile_tests() {
     t.compile_fail("tests/ui/fail/15-multiple-storage-structs.rs");
     t.compile_fail("tests/ui/fail/16-storage-impl-ident-conflict.rs");
     t.compile_fail("tests/ui/fail/17-conflicting-ink-markers.rs");
+    t.compile_fail("tests/ui/fail/18-conflicting-ink-markers-2.rs");
 }

lang2/macro/tests/ui/fail/18-conflicting-ink-markers-2.rs

+#![feature(proc_macro_hygiene)]
+
+use ink_lang2 as ink;
+
+#[ink::contract(version = "0.1.0")]
+mod noop {
+    #[ink(storage)]
+    struct Noop {}
+
+    #[ink(event)]
+    #[ink(storage)] // We cannot have #[ink(event)] if we already have #[ink(storage)]
+    struct Event {}
+
+    impl Noop {
+        #[ink(constructor)]
+        fn new(&mut self) {}
+
+        #[ink(message)]
+        fn noop(&self) {}
+    }
+}
+
+fn main() {}

lang2/macro/tests/ui/fail/18-conflicting-ink-markers-2.stderr

+error: invalid ink! attribute found for `#[ink(event)]` struct
+  --> $DIR/18-conflicting-ink-markers-2.rs:11:10
+   |
+11 |     #[ink(storage)] // We cannot have #[ink(event)] if we already have #[ink(storage)]
+   |          ^^^^^^^^^