provenance/Dockerfile: Fix warning about env instructions

Refs. sysadm-environment#5608

apps/swh-provenance/Dockerfile

@@ -39,15 +39,15 @@ COPY --from=rust_build /usr/local/cargo/bin/swh-provenance* /usr/local/bin/
 USER ${user}
 ENV SWH_CONFIG_FILENAME=${configdir}/config.yml
 # Default to be a rpc service
-ENV PORT 5014
-ENV PROVENANCE_TYPE "rpc"
+ENV PORT=5014
+ENV PROVENANCE_TYPE="rpc"
 # Possible other value for grpc kind
 # ENV PORT 50141
 # ENV PROVENANCE_TYPE "grpc"
 EXPOSE $PORT
 # For rpc type, this maps directly to gunicorn env variables
-ENV WORKERS 8
-ENV THREADS 2
-ENV TIMEOUT 3600
+ENV WORKERS=8
+ENV THREADS=2
+ENV TIMEOUT=3600
 
 ENTRYPOINT ["/opt/swh/entrypoint.sh"]