Prevent overlays from being improperly used as format strings

`wwctl overlay show --render` shows the rendered overlay with
`wwlog.Info`, but that caused it to be processed as a format string.
This passes an explicit format string first, and then includes the
rendered overlay as a variable to the formatter.

- Fixes #1363

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

internal/app/wwctl/overlay/show/main.go

@@ -113,7 +113,7 @@ func CobraRunE(cmd *cobra.Command, args []string) error {
 			wwlog.Info("backupFile: %v\nwriteFile: %v", backupFile, writeFile)
 			wwlog.Info("Filename: %s\n", destFileName)
 		}
-		wwlog.Info(outBuffer.String())
+		wwlog.Info("%s", outBuffer.String())
 	}
 	return nil
 }