[Bug]: Missing Composer dependencies after upgrading to 4.0.0

Description of the bug

After upgrading the plugin to version 4.0.0, WordPress crashes due to missing Composer dependencies.

Reproduction instructions

1. Install plugin in version 3.10.0
2. Upgrade to 4.0.0
3. Website crashes

(A fresh install probably works, too)

Expected behavior

Plugin doesn't crash, dependencies are present.

Environment info

• Chrome 107, macOS
• PHP 7.4, PHP 8.0, PHP 8.1
• Ubuntu 20.04

Relevant log output

[Wed Nov 16 13:08:47.194013 2022] [proxy_fcgi:error] [pid 2515441] [client XXXXXXXXXX:31216] AH01071: Got error 'PHP message: PHP Warning:  require(/var/www/example.com/wp-content/plugins/backwpup/vendor/composer/../amphp/amp/lib/functions.php): failed to open stream: No such file or directory in /var/www/example.com/wp-content/plugins/backwpup/vendor/composer/autoload_real.php on line 59PHP message: PHP Fatal error:  require(): Failed opening required '/var/www/example.com/wp-content/plugins/backwpup/vendor/composer/../amphp/amp/lib/functions.php' (include_path='/var/www/example.com/wp-content/plugins/backwpup/vendor/pear/pear_exception:/var/www/example.com/wp-content/plugins/backwpup/vendor/pear/console_getopt:/var/www/example.com/wp-content/plugins/backwpup/vendor/pear/pear-core-minimal/src:/var/www/example.com/wp-content/plugins/backwpup/vendor/pear/archive_tar:.:/usr/share/php') in /var/www/example.com/wp-content/plugins/backwpup/vendor/composer/autoload_real.php on line 59', referer: http://example.com/wp-login.php

Additional context

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

Reproduce the upgrade from BackWPup 3.10.0 to 4.0.0 and inspect vendor/composer/autoload_real.php together with the missing vendor/composer/../amphp/amp/lib/functions.php path. Check how dependencies are included in the release package. Done means both upgrades and fresh installs include the required dependencies without the WordPress crash.