Pin gVisor to the last working release

Temporarily pin gVisor to the latest working version
(`release-20240826.0`), since the latest one breaks our container image.

Refs #928

Dockerfile

@@ -88,7 +88,9 @@ FROM alpine:latest
 RUN apk --no-cache -U upgrade && \
  apk --no-cache add python3
 
-RUN GVISOR_URL="https://storage.googleapis.com/gvisor/releases/release/latest/$(uname -m)"; \
+# Temporarily pin gVisor to the latest working version (release-20240826.0).
+# See: https://github.com/freedomofpress/dangerzone/issues/928
+RUN GVISOR_URL="https://storage.googleapis.com/gvisor/releases/release/20240826/$(uname -m)"; \
  wget "${GVISOR_URL}/runsc" "${GVISOR_URL}/runsc.sha512" && \
  sha512sum -c runsc.sha512 && \
  rm -f runsc.sha512 && \