How to run UPX when releasing only?

[bgr]

I spent quite a bit of time trying out various combinations of syntax like the following:

upx:
  - enabled: "{{ not .IsSnapshot }}"

but I couldn't figure it out, it's always an error like cannot unmarshal !!str `{{...` into bool.

Is there a way to do this, or is using such syntax not valid for that field?
Is there another way to have UPX disabled for local builds while developing?

[caarlos0]

It isn't possible right now, just implemented it though: #4269

Will be available in the next release.