Actions: Support YAML comments.

actions/ql/lib/codeql/actions/ast/internal/Ast.qll

@@ -1920,3 +1920,5 @@ private YamlMappingLikeNode resolveMatrixAccessPath(
     else result = resolveMatrixAccessPath(newRoot, rest)
   )
 }
+
+class Comment = YamlComment;

actions/ql/lib/codeql/actions/ast/internal/Yaml.qll

@@ -52,6 +52,12 @@ private module YamlSig implements LibYaml::InputSig {
   class ParseErrorBase extends LocatableBase, @yaml_error {
     string getMessage() { yaml_errors(this, result) }
   }
+
+  class CommentBase extends LocatableBase, @yaml_comment {
+    string getText() { yaml_comments(this, result, _) }
+
+    override string toString() { yaml_comments(this, _, result) }
+  }
 }
 
 import LibYaml::Make<YamlSig>