helm: bump default image tag to v3.2.0 (#14476)

chart/values.yaml.template

@@ -4,7 +4,7 @@ image:
   repository: tootsuite/mastodon
   pullPolicy: Always
   # https://hub.docker.com/r/tootsuite/mastodon/tags
-  tag: v3.1.5
+  tag: v3.2.0
   # alternatively, use `latest` for the latest release or `edge` for the image
   # built from the most recent commit
   #