github: enable docker feature
github: enable docker feature

Change-Id: I3251dbd83f3724b28b5732f4bc825288eba6afcf
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/5141
Reviewed-by: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>

cuelang/cue