[Dovecot] Update to 2.3.21

data/Dockerfiles/dovecot/Dockerfile

@@ -3,7 +3,7 @@ LABEL maintainer "The Infrastructure Company GmbH <info@servercow.de>"
 
 ARG DEBIAN_FRONTEND=noninteractive
 # renovate: datasource=github-tags depName=dovecot/core versioning=semver-coerced extractVersion=^v(?<version>.*)$
-ARG DOVECOT=2.3.20
+ARG DOVECOT=2.3.21
 # renovate: datasource=github-releases depName=tianon/gosu versioning=semver-coerced extractVersion=^v(?<version>.*)$
 ARG GOSU_VERSION=1.16
 ENV LC_ALL C