[cxx-interop] Relax a SILVerifier assertion for immortal reference types
Immortal C++ foreign reference types get TrivialTypeLowering instead of ReferenceTypeLowering, since they do not have retain/release lifetime operations. This was tripping up an assertion in SILVerifier.
rdar://147251759 / resolves https://github.com/swiftlang/swift/issues/80065
(cherry picked from commit 2e3df1c0f32eeb8a99a230ba776fde3c0fc35e5d)