fix: hide masked value (#668)

* fix: hide masked value

The ::add-mask:: command output logs the value to be masked.
This does expose critical information which should be hidden from
the output.

* Add test to not output secret in add-mask command

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

pkg/runner/command.go

@@ -54,7 +54,7 @@ func (rc *RunContext) commandHandler(ctx context.Context) common.LineHandler {
 		case "error":
 			logger.Infof("  \U00002757  %s", line)
 		case "add-mask":
-			logger.Infof("  \U00002699  %s", line)
+			logger.Infof("  \U00002699  %s", "***")
 		case "stop-commands":
 			resumeCommand = arg
 			logger.Infof("  \U00002699  %s", line)