Reject common phrases like "guten morgen"

In German, "morgen" is used for "tomorrow" and there is a rule for that:

https://github.com/facebook/duckling/blob/7520daaeba28691cda8e1b5c3d946028a28fb64b/Duckling/Time/DE/Rules.hs#L40

Unfortunately, this means that phrases like "guten morgen" are interpreted as "tomorrow", despite it being a common phrase that has nothing to do with time. I would like to add some kind of rule that detects this pattern and always rejects it.

My initial attempt used negative lookbehinds like `(?