mytarc: chmod 444 .sha256sum file

The .sha256sum file should be given 444 permissions too.
Signed-off-by: Cédric Marie <cedric@hjuvi.fr.eu.org>

scripts/mytarc

@@ -3,7 +3,7 @@
 # mytarc - Create an archive (.tar[.xz] file) with the content of a directory
 # This file is part of Painted Shell - Shell configuration and scripts.
 #
-# Written in 2013-2019 by Cédric Marie
+# Written in 2013-2020 by Cédric Marie
 #
 # To the extent possible under law, the author(s) have dedicated all copyright
 # and related and neighboring rights to this software to the public domain
@@ -76,5 +76,6 @@ chmod 444 $output_file
 printf "\033[1mOutput file:\033[0m $output_file\n"
 if [ $option_sha256sum -eq 1 ]; then
     sha256sum $output_file > $output_file.sha256sum
+    chmod 444 $output_file.sha256sum
     printf "           + $output_file.sha256sum\n"
 fi