Add the case in duplicate issue (#4806) to the idempotent tests

Author: ChinYing-Li

tests/source/issue-4312.rs

@@ -1,8 +1,22 @@
+// issue 4312
 fn main() {
     /* " */
     println!("Hello, world!");
     /* abc " */
     println!("Hello, world!");
     /* " abc */
     println!("Hello, world!");
+    let y = 4;
+    let x = match 1 + y == 3 {
+        True => 3,
+        False => 4,
+        /* " unreachable */
+    };
+}
+
+// issue 4806
+enum X {
+    A,
+    B,
+    /*"*/
 }

tests/target/issue-4312.rs

@@ -1,8 +1,22 @@
+// issue 4312
 fn main() {
     /* " */
     println!("Hello, world!");
     /* abc " */
     println!("Hello, world!");
     /* " abc */
     println!("Hello, world!");
+    let y = 4;
+    let x = match 1 + y == 3 {
+        True => 3,
+        False => 4,
+        /* " unreachable */
+    };
+}
+
+// issue 4806
+enum X {
+    A,
+    B,
+    /*"*/
 }