.github/workflow: use buildx v0.9.1 to fix fly deploys

Fixes #51

Signed-off-by: Will Norris <[email protected]>

Author: willnorris

.github/workflows/docker.yml

@@ -31,6 +31,9 @@ jobs:
 
     - name: Setup Docker buildx
       uses: docker/setup-buildx-action@8c0edbc76e98fa90f69d9a2c020dcb50019dc325 # v2.2.1
+      with:
+        # use buildx v0.9.1 (https://community.fly.io/t/10171/19)
+        version: v0.9.1
 
     - name: Log into registry ${{ env.REGISTRY }}
       uses: docker/login-action@f4ef78c080cd8ba55a85445d5b36e214a81df20a # v2.1.0