Fixed incorrect self-signup setting for portal modal

no issue

- Portal modal was using incorrect `allowSelfSignup` value post settings refactor
- Updated to use correct setting for free signup to correctly disable/enable checkbox

app/components/gh-members-lab-setting.hbs

@@ -394,9 +394,6 @@
 
 {{#if this.showMembersModalSettings}}
     <GhFullscreenModal @modal="members-modal-settings"
-        @model={{hash
-            allowSelfSignup=this.allowSelfSignup
-        }}
         @close={{action "closeMembersModalSettings"}}
         @modifier="full-overlay portal-settings" />
 {{/if}}

app/components/modal-members-modal-settings.hbs

@@ -41,7 +41,7 @@
                                         checked={{this.isFreeChecked}}
                                         id="free-plan"
                                         name="free-plan"
-                                        disabled={{not this.subscriptionSettings.allowSelfSignup}}
+                                        disabled={{not this.allowSelfSignup}}
                                         class="gh-input post-settings-featured"
                                         onclick={{action "toggleFreePlan" value="target.checked"}}
                                         data-test-checkbox="featured"

app/components/modal-members-modal-settings.js

@@ -23,7 +23,7 @@ export default ModalComponent.extend({
 
     signupButtonText: boundOneWay('settings.portalButtonSignupText'),
     buttonIcon: boundOneWay('settings.portalButtonIcon'),
-    allowSelfSignup: alias('model.allowSelfSignup'),
+    allowSelfSignup: alias('settings.membersAllowFreeSignup'),
 
     isStripeConfigured: reads('membersUtils.isStripeEnabled'),