Add caching information to block.

Closes #3530782

src/Plugin/Block/DrupalOrgDocumentationIssue.php

@@ -78,9 +78,17 @@ class DrupalOrgDocumentationIssue extends BlockBase implements ContainerFactoryP
         ],
       ]);
 
+      $cache_tags = [
+        'node:' . $node->id(),
+      ];
+
       return [
         '#theme' => 'drupalorg_documentation_issue_submission',
         '#url' => $url->toString(),
+        '#cache' => [
+          'contexts' => ['url'],
+          'tags' => $cache_tags,
+        ],
       ];
     }