Use thread-safe types to store the LOG_PROTOCOL_WARN severity

Fixes a race condition; resolves 23954.

src/test/fuzz/fuzzing_common.c

@@ -152,6 +152,8 @@ main(int argc, char **argv)
     }
   }
 
+  init_protocol_warning_severity_level();
+
   {
     log_severity_list_t s;
     memset(&s, 0, sizeof(s));

src/test/testing_common.c

@@ -278,6 +278,7 @@ main(int c, const char **v)
     s.masks[LOG_WARN-LOG_ERR] |= LD_BUG;
     add_stream_log(&s, "", fileno(stdout));
   }
+  init_protocol_warning_severity_level();
 
   options->command = CMD_RUN_UNITTESTS;
   if (crypto_global_init(accel_crypto, NULL, NULL)) {