Don't use singleton for getForm

When using Injector to create a singleton constructor arguments are
ignored. This causes getForm to fail as SAMLLoginForm requires
constructor arguments.

src/Control/SAMLController.php

@@ -354,6 +354,6 @@ public function getLogger()
      */
     public function getForm()
     {
-        return Injector::inst()->get(SAMLLoginForm::class, true, [$this, SAMLAuthenticator::class, 'LoginForm']);
+        return Injector::inst()->get(SAMLLoginForm::class, false, [$this, SAMLAuthenticator::class, 'LoginForm']);
     }
 }

tests/php/Control/SAMLControllerTest.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace SilverStripe\SAML\Tests\Control;
+
+use SilverStripe\Dev\SapphireTest;
+use SilverStripe\SAML\Control\SAMLController;
+
+class SAMLControllerTest extends SapphireTest
+{
+    public function testGetForm(): void
+    {
+        $controller = new SAMLController();
+
+        $form = $controller->getForm();
+
+        $this->assertNotNull($form);
+    }
+}