bootstrap, containers: hard-code buildx version

work around docker/build-push-action#755

Author: classabbyamp

.github/workflows/bootstrap.yml

@@ -30,6 +30,8 @@ jobs:
         uses: docker/setup-qemu-action@v1
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1
+        with:
+          version: v0.9.1
       - name: Login to GCHR
         uses: docker/login-action@v1
         with:

.github/workflows/containers.yml

@@ -36,6 +36,8 @@ jobs:
         uses: docker/setup-qemu-action@v1
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1
+        with:
+          version: v0.9.1
       - name: Login to GCHR
         uses: docker/login-action@v1
         with: