go-neb isn't functional on linux

After providing the access token created for the bot user to go-neb via a http api call, and enabling the echo service, the bot doesn't react upon inviting to a room.

Logs show that go-neb tries to connect to synapse container for sync, but that connection attempt is refused. go-neb was able to ping the synapse container from its container though:

```
docker exec -it go-neb-container-id /bin/sh
ping matrix-env-synapse
```

This issue is specific to linux (tried on Arch linux) and works without an issue on MacOS.

Start by reproducing the Linux setup with the Docker Compose containers, then inspect the go-neb logs and its attempted connection to the synapse container. Compare the refused sync connection with the successful ping to matrix-env-synapse and with the reported macOS behavior. Done means the echo bot responds after being invited to a room on Linux.

Written by the indexing model from the issue text.