MDL-73601 lib: Normalize readme_moodle.txt file name

lib/classes/check/environment/publicpaths.php

@@ -127,7 +127,7 @@ class publicpaths extends check {
             [
                 'pattern'   => 'readme.txt',
                 '404'       => [
-                    'lib/scssphp/moodle_readme.txt',
+                    'lib/scssphp/readme_moodle.txt',
                     'mod/resource/readme.txt',
                 ],
             ],

lib/scssphp/readme_moodle.txt

@@ -5,7 +5,7 @@ Downloaded from: https://github.com/scssphp/scssphp
 
 Import procedure:
 
-- Delete everything from this directory except moodle_readme.txt (this file).
+- Delete everything from this directory except readme_moodle.txt (this file).
 - Copy all the files from the folder 'src' to this directory.
 - Copy the license file from the project root.
 - Review the local changes defined below, if any. Reapply