Fix compatibility with php8

[marcpaulchand]

Hello

I tried to setup it with php8.

I got this error message :

3831#3831: *1 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Array and string offset access syntax with curly braces is no longer supported in /usr/share/yubikey-ksm/ykksm-utils.php on line 36" while rea
ding response header from upstream, client: ::1, server: , request: "GET /wsapi/decrypt.php?otp=ccccccdvlncufehgjirkkgnfhrkrrhnrblebciiivjug HTTP/1.1", upstream: "fastcgi://unix:/var/run/php-fpm8/php-fpm.sock:", host: "localhost"

So i adjust line36 in order to get te correct answer with my wget.

Before

wget -q -O - 'http://localhost/wsapi/decrypt.php?otp=xxxxxxxxxxxxxehgjirkkgnfhrkrrhnrblebciiivjug'
ERR Database error

After change

wget -q -O - 'http://localhost/wsapi/decrypt.php?otp=xxxxxxxxxxxxxehgjirkkgnfhrkrrhnrblebciiivjug'
ERR Unknown yubikey