actually add imul test case

.github/workflows/ci.yml

@@ -2,13 +2,7 @@ name: CI
 
 on:
   pull_request:
-    paths:
-      - ".github/workflows/ci.yml"
-      - "**.zig"
   push:
-    paths:
-      - ".github/workflows/ci.yml"
-      - "**.zig"
     branches:
       - main
   schedule:

test/imul/main.nat

@@ -0,0 +1,5 @@
+const main = fn () s32 {
+    const a: s32 = 5;
+    const b: s32 = 4;
+    return 5 * 4 - a * b;
+}