Within an htaccess file, the scope of the <Files>
directive only applies to that directory (I guess to avoid confusion when rules/directives in the htaccess of subdirectories get applied superceding ones from the parent).
So you can have:
<Files "log.txt">
Order Allow,Deny
Deny from all
</Files>
For Apache 2.4+, you'd use:
<Files "log.txt">
Require all denied
</Files>
In an htaccess file in your inscription
directory. Or you can use mod_rewrite to sort of handle both cases deny access to htaccess file as well as log.txt:
RewriteRule /?\.htaccess$ - [F,L]
RewriteRule ^/?inscription/log\.txt$ - [F,L]