Test Generator: `CollectionName` is ignored by Sync outbox templates, so sync tests are never serialised

## Summary

`OutboxConfiguration.CollectionName` is intended to render an xUnit `[Collection(...)]` attribute so tests sharing infrastructure do not run concurrently. It is honoured by the **Async** outbox templates but **not by any of the Sync** ones, so the generated sync outbox tests carry no `[Collection]` and can run in parallel against the same store.

## Evidence

From `tools/Paramore.Brighter.Test.Generator/Templates`:

```
$ grep -rl "CollectionName" Templates/Outbox/Async/ | wc -l
12
$ grep -rl "CollectionName" Templates/Outbox/Sync/ | wc -l
0
```

The messaging gateway templates (`Reactor/` and `Proactor/`) both honour it, so the outbox `Sync` set is the odd one out.

Configs that set `CollectionName` on an outbox and are silently getting no serialisation on their sync tests include `tests/Paramore.Brighter.MySQL.Tests/test-configuration.json` (`MySQLTextOutbox`, `MySQLBinaryOutbox`) and the MSSQL/PostgreSQL equivalents.

## Impact

A likely source of CI flakiness: two sync outbox test classes over the same store can interleave. It would also be masked today wherever the outbox is configured with the singular `Outbox` form, since no sync tests are generated at all (see the sibling issue on that).

## Expected

The `Sync` outbox templates should emit `[Collection(...)]` the same way the `Async` ones do:

```liquid
{% if CollectionName != null %}[Collection("{{CollectionName}}")]{% endif %}
```

## Suggested fix

Add the conditional to the 12 templates in `Templates/Outbox/Sync/`, then regenerate all projects with `./generate-test.sh`.

## Notes

Found while documenting the generator for `docs/factories/tests`, where the gap is currently noted as a known defect.