Add QUIC_EXPORT_PRIVATE to RawSha256 method since it is used directly in third_party/quic/quic_transport/web_transport_fingerprint_proof_verifier_test.cc

PiperOrigin-RevId: 411146926

quic/core/quic_utils.h

diff --git a/quic/core/quic_utils.h b/quic/core/quic_utils.h
index a7bfc70..9b5c6ff 100644
--- a/quic/core/quic_utils.h
+++ b/quic/core/quic_utils.h
@@ -257,7 +257,7 @@
 QuicByteCount MemSliceSpanTotalSize(absl::Span<QuicMemSlice> span);
 
 // Computes a SHA-256 hash and returns the raw bytes of the hash.
-std::string RawSha256(absl::string_view input);
+QUIC_EXPORT_PRIVATE std::string RawSha256(absl::string_view input);
 
 template <typename Mask>
 class QUIC_EXPORT_PRIVATE BitMask {