skymarshal: behavior: fix default local username prompt
The path that was checked when setting the default username prompt for
local logins did not match the full request path of the local login
page. This meant that the default username prompt was never being set.
concourse/concourse#8361
{{ template "header.html" . }}
{{ $usernamePrompt := .UsernamePrompt | lower }}
-{{ if eq .ReqPath "/sky/issuer/auth/local" }}
+{{ if eq .ReqPath "/sky/issuer/auth/local/login" }}
{{ $usernamePrompt = "username" }}
{{ end }}
