[prometheus] Use current_option() instead of deprecated .state for select entities (#12079)

esphome/components/prometheus/prometheus_handler.cpp

@@ -726,7 +726,7 @@ void PrometheusHandler::select_row_(AsyncResponseStream *stream, select::Select
     stream->print(ESPHOME_F("\",name=\""));
     stream->print(relabel_name_(obj).c_str());
     stream->print(ESPHOME_F("\",value=\""));
-    stream->print(obj->state.c_str());
+    stream->print(obj->current_option());
     stream->print(ESPHOME_F("\"} "));
     stream->print(ESPHOME_F("1.0"));
     stream->print(ESPHOME_F("\n"));