`Test_ProxyServer_Headers` never passed `--http-address`, so it bound to
the default `127.0.0.1:3000`.
`TestWorkspaceProxy_Server_PrometheusEnabled`
used `RandomPort(t)` for `--http-address` (a drive-by from #14972 which
was
fixing the Prometheus port).
Both now use `--http-address :0`. `ConfigureHTTPServers` calls
`net.Listen("tcp", ":0")` and holds the listener open, so there is no
TOCTOU window. Neither test connects to the HTTP listener, so the
assigned port is irrelevant. This matches `cli/server_test.go` where
`:0` is used throughout.
Mathias Fredriksson
338d30e4c4