Add two extra test cases

Author: StevenWong12

Tests/SwiftParserTest/translated/OperatorDeclTests.swift

@@ -479,6 +479,29 @@ final class OperatorDeclTests: XCTestCase {
       ]
     )
   }
+  
+  func testOperatorDecl124() {
+    assertParse(
+      """
+      1️⃣@objc
+      postfix operator ++: PrecedenceGroup
+      """,
+      diagnostics: [
+        DiagnosticSpec(message: "unexpected code '@objc' before operator declaration")
+      ]
+    )
+  }
+  
+  func testOperatorDecl125() {
+    assertParse(
+      """
+      1️⃣mutating postfix operator --: UndefinedPrecedenceGroup
+      """,
+      diagnostics: [
+        DiagnosticSpec(message: "unexpected code 'mutating' before operator declaration")
+      ]
+    )
+  }
 
   func testIdentifierAsOperatorName() {
     assertParse(