[AutoDiff] Add missing REQUIRES: asserts to test. (swiftlang#33874)

`test/AutoDiff/validation-test/optional-property.swift` uses
`-Xllvm -debug-only=differentiation`, which requires assertions enabled.

Author: dan-zheng

test/AutoDiff/validation-test/optional-property.swift

@@ -1,6 +1,7 @@
 // RUN: %target-run-simple-swift
 // RUN: %target-swift-emit-sil -Xllvm -debug-only=differentiation -o /dev/null 2>&1 %s | %FileCheck %s
 // REQUIRES: executable_test
+// REQUIRES: asserts
 
 // Test differentiation of `Optional` properties.