I am having this issues randomly today too. I woke up to two GitHub action jobs taking 6 hours then being cancelled (which annoyingly used up a chunk of my minutes 
).
The build doesn’t get pass this step
Run flyctl deploy --remote-only --app [my-app]
6 ==> Verifying app config
7 --> Verified app config
8 ==> Building image
9 Waiting for remote builder fly-builder-bitter-silence-192...
10 Remote builder fly-builder-bitter-silence-192 ready
11 ==> Creating build context
12 --> Creating build context done
13 ==> Building image with Docker
14 --> docker host: 20.10.12 linux x86_64
I have rerun the build a few times this morning and it continues to get stalled here. I stop it after it attempts for 5mins on this step. My region I am attempting to deploy to is syd.