Remove obsolete reference to SafeMarkup::set() in LinkGeneratorTest documentation

Problem/Motivation

Some documentation around SafeMarkup was left in the test comments.

+++ b/core/tests/Drupal/Tests/Core/Utility/LinkGeneratorTest.php
@@ -364,16 +364,19 @@ public function testGenerateWithHtml() {
+    // Test that safe HTML is output inside the anchor tag unescaped. The
+    // SafeMarkup::set() call is an intentional unit test for the interaction
+    // between SafeMarkup and the LinkGenerator.

Proposed resolution

Rewrite the addition added by #2501705: Remove SafeMarkup::set() in LinkGenerator and document SafeMarkup::set() in LinkGeneratorTest because there is no longer SafeMarkup there and instead SafeStringInterface.

Remaining tasks

User interface changes

API changes

Data model changes

Follow-up to #2501705: Remove SafeMarkup::set() in LinkGenerator and document SafeMarkup::set() in LinkGeneratorTest

Beta phase evaluation