Add masks for multiline secrets from ::add-mask:: (#1521)

* Add mask for multiline secrets.

* .

src/Runner.Worker/ActionCommandManager.cs

@@ -381,6 +381,13 @@ namespace GitHub.Runner.Worker
 
                 HostContext.SecretMasker.AddValue(command.Data);
                 Trace.Info($"Add new secret mask with length of {command.Data.Length}");
+
+                // Also add each individual line. Typically individual lines are processed from STDOUT of child processes.
+                var split = command.Data.Split(new[] { '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
+                foreach (var item in split)
+                {
+                    HostContext.SecretMasker.AddValue(item);
+                }
             }
         }
     }