senza update changes nothing if only tags changed

[Andras Vaczi]

Changing an existing tag to some other value results in a NO UPDATE upon senza update.

SenzaInfo:
  StackName: spilo
  Tags:
    - SpiloCluster: "{{Arguments.version}}"
    - Environment: "live" # changed from something else

senza update this.yaml this
Generating Cloud Formation template.. OK
Updating Cloud Formation stack spilo-loungemarketingblacklist.. NO UPDATE

Might be related to #413, but there the end is somehow missing.