[ssl] Downgrade SSL handshake failure log to INFO. (grpc#38058)

This log can be hit under normal circumstances (e.g. a client has an expired cert and authenticates to the server), so this should be an INFO-level log rather than an ERROR-level log.

Closes grpc#38058

COPYBARA_INTEGRATE_REVIEW=grpc#38058 from matthewstevenson88:downgrade23 1cbdd5a
PiperOrigin-RevId: 693375018

Author: matthewstevenson88

src/core/tsi/ssl_transport_security.cc

@@ -1662,9 +1662,9 @@ static tsi_result ssl_handshaker_do_handshake(tsi_ssl_handshaker* impl,
           const char* verify_err = X509_verify_cert_error_string(verify_result);
           verify_result_str = absl::StrCat(": ", verify_err);
         }
-        LOG(ERROR) << "Handshake failed with fatal error "
-                   << grpc_core::SslErrorString(ssl_result) << ": " << err_str
-                   << verify_result_str;
+        LOG(INFO) << "Handshake failed with error "
+                  << grpc_core::SslErrorString(ssl_result) << ": " << err_str
+                  << verify_result_str;
         if (error != nullptr) {
           *error = absl::StrCat(grpc_core::SslErrorString(ssl_result), ": ",
                                 err_str, verify_result_str);