Getting `Unable to query for supported registration methods` on registration page

**Describe the bug**
After running ./setup.sh, `docker compose up -d`, error message is displayed on
registration page.

**To Reproduce**
Steps to reproduce the behaviour:
1. Go to https://element.local.test/#/register
2. See `Unable to query for supported registration methods.` message printed
below `Create Account` header. Note that fields to specify username and
password are not present.

Element sends this request (trimmed from non-necessary headers for brevity):

```sh
$ curl 'https://matrix.local.test/_matrix/client/v3/register' -X POST -H
'Content-Type: application/json' -H 'Origin: https://element.local.test'
--data-raw '{"initial_device_display_name":"element.local.test: Firefox on
Linux"}'
```
```
{"errcode":"M_UNKNOWN","error":"Invalid username"}
```

**Expected behaviour**
There should be no errors on registration page, and it should be possible to
register an account.

**Desktop (please complete the following information):**
- OS: Linux
- Browser LibreWolf (Firefox fork with tracking removed)
- Version 134.0.2

Start with setup.sh and the docker-compose configuration, then reproduce the registration-page error at https://element.local.test/#/register. Inspect the /_matrix/client/v3/register response and the related service logs to determine why registration receives Invalid username. Done means the registration page shows its username and password fields and a test account can be created.

Written by the indexing model from the issue text.