Correctly escape username pattern regex

Without the escaping, the backslash doesn't get renderet in the frontend
which leads to some browsers (chrome >= 114?) just allowing every input.

app/views/registrations/_form.haml

@@ -32,7 +32,7 @@
                    placeholder: t("registrations.new.username"),
                    title:       t("registrations.new.enter_username"),
                    required:    true,
-                   pattern:     "[A-Za-z0-9_.\-]+",
+                   pattern:     "[A-Za-z0-9_.\\-]+",
                    aria:        {labelledby: "usernameLabel"}
 
     - if mobile

app/views/sessions/_form.haml

@@ -19,7 +19,7 @@
                    placeholder: t("registrations.new.username"),
                    class: "input-block-level form-control",
                    required: true,
-                   pattern: "[A-Za-z0-9_.@\-]+",
+                   pattern: "[A-Za-z0-9_.@\\-]+",
                    autocapitalize: "none",
                    autocorrect: "off",
                    autofocus: true,