```
$ go get -u github.com/matrix-org/gomatrixserverlib@dmr/msc-3706-stable-identifiers
go: downloading github.com/matrix-org/gomatrixserverlib v0.0.0-20230112185427-4f65e88d2a5b
go: downloading golang.org/x/crypto v0.5.0
go: downloading github.com/matrix-org/gomatrix v0.0.0-20220926102614-ceba4d9f7530
go: downloading github.com/matrix-org/util v0.0.0-20221111132719-399730281e66
go: downloading github.com/tidwall/gjson v1.14.4
go: downloading golang.org/x/sys v0.4.0
go: downloading github.com/tidwall/pretty v1.2.1
go: downloading golang.org/x/text v0.6.0
go: downloading golang.org/x/net v0.5.0
go: downloading golang.org/x/tools v0.1.12
go: downloading github.com/miekg/dns v1.1.50
go: downloading gopkg.in/h2non/gock.v1 v1.1.2
go: downloading github.com/stretchr/testify v1.8.0
go: upgraded github.com/matrix-org/gomatrix v0.0.0-20210324163249-be2af5ef2e16 => v0.0.0-20220926102614-ceba4d9f7530
go: upgraded github.com/matrix-org/gomatrixserverlib v0.0.0-20220830164018-c71e518537a2 => v0.0.0-20230112185427-4f65e88d2a5b
go: upgraded github.com/matrix-org/util v0.0.0-20200807132607-55161520e1d4 => v0.0.0-20221111132719-399730281e66
go: upgraded github.com/tidwall/gjson v1.14.3 => v1.14.4
go: upgraded github.com/tidwall/pretty v1.2.0 => v1.2.1
go: upgraded golang.org/x/crypto v0.0.0-20220829220503-c86fa9a7ed90 => v0.5.0
go: upgraded golang.org/x/net v0.0.0-20220520000938-2e3eb7b945c2 => v0.5.0
go: upgraded golang.org/x/sys v0.0.0-20220829200755-d48e67d00261 => v0.4.0
go: upgraded golang.org/x/tools v0.1.9 => v0.1.12
go: upgraded gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b =>
v3.0.1
```

See matrix-org/gomatrixserverlib#344

AFAICS passing nil means that the server isn't going to accept any
vhosting shenanigans.

matrix-org/gomatrixserverlib@900369e

there's probably a neater way to not write
`gomatrixserverlib.ServerName` but idk what the best thing to do is here.

missed this one because struct fields are optional(?)