makefile: make clean to remove dashboard temp (#7586)

close #7585

Signed-off-by: husharp <jinhao.hu@pingcap.com>

Co-authored-by: ti-chi-bot[bot] <108142056+ti-chi-bot[bot]@users.noreply.github.com>

Makefile

@@ -305,6 +305,7 @@ clean-test:
 clean-build:
 	# Cleaning building files...
 	rm -rf .dashboard_download_cache/
+	rm -rf .dashboard_build_temp/
 	rm -rf $(BUILD_BIN_PATH)
 	rm -rf $(GO_TOOLS_BIN_PATH)