Add substructure test for deinit parsing

Author: ahoppen

Tests/SwiftParserTest/translated/InitDeinitTests.swift

@@ -1,5 +1,7 @@
 // This test file has been translated from swift/test/Parse/init_deinit.swift
 
+import SwiftSyntax
+
 import XCTest
 
 final class InitDeinitTests: XCTestCase {
@@ -380,7 +382,13 @@ final class InitDeinitTests: XCTestCase {
         deinit
         final func foo()
       }
-      """
+      """,
+      substructure: Syntax(DeinitializerDeclSyntax(
+        attributes: nil,
+        modifiers: nil,
+        deinitKeyword: .deinitKeyword(),
+        body: nil
+      ))
     )
   }
 }