Merge pull request #188 from cybozu-go/bump-runner-version

Bump runner version from 2.320.0 to 2.321.0

Dockerfile

@@ -19,7 +19,7 @@ LABEL org.opencontainers.image.source="https://github.com/cybozu-go/meows"
 
 # Even if the version of the runner is out of date, it will self-update at job execution time. So there is no problem to update it when you notice.
 # TODO: Until https://github.com/cybozu-go/meows/issues/137 is fixed, update it manually.
-ARG RUNNER_VERSION=2.320.0
+ARG RUNNER_VERSION=2.321.0
 
 ENV DEBIAN_FRONTEND=noninteractive
 # hadolint ignore=DL3015