Add QUIC_EXPORT_PRIVATE to quic::PublicKeyTypeToString.

PiperOrigin-RevId: 421093299

quic/core/crypto/certificate_view.h

diff --git a/quic/core/crypto/certificate_view.h b/quic/core/crypto/certificate_view.h
index e546bf6..5b3c8c7 100644
--- a/quic/core/crypto/certificate_view.h
+++ b/quic/core/crypto/certificate_view.h
@@ -42,7 +42,7 @@
   kEd25519,
   kUnknown,
 };
-std::string PublicKeyTypeToString(PublicKeyType type);
+QUIC_EXPORT_PRIVATE std::string PublicKeyTypeToString(PublicKeyType type);
 
 // CertificateView represents a parsed version of a single X.509 certificate. As
 // the word "view" implies, it does not take ownership of the underlying strings