PHP8 compatibility

If anyone is still using this plugin, there is a problem with PHP8.

In multilingual-press/inc/installation/Mlp_Self_Check.php on line 290 you need to change the line:

if ( version_compare( $current_version, $last_version, '=<' ) ) {

to:

if ( version_compare( $current_version, $last_version, '<=' ) ) {

Please note the small change in the last parameter (“=<” changed to “<=”).

See: https://www.php.net/manual/de/function.version-compare.php