Fix premium plugin detection

When mounted the plugin was mounted directly to the plugin folder get_plugins() function
ignored it. We had a similar issue in the past when we were using a softlink.
Copying the plugin is a workaround that fixes the issue.
[MAILPOET-4662]

mailpoet/tests/docker/codeception/docker-entrypoint.sh

@@ -192,6 +192,8 @@ if [[ $MULTISITE == "1" ]]; then
 fi
 
 if [[ $CIRCLE_JOB == *"_with_premium_"* ]]; then
+  # Copy MailPoet Premium to plugin path
+  cp -r -n /project/mailpoet-premium /wp-core/wp-content/plugins/mailpoet-premium
   # Activate MailPoet Premium
   wp plugin activate mailpoet-premium
 fi

mailpoet/tests/docker/docker-compose.yml

@@ -12,7 +12,7 @@ services:
       - mailhog-data:/mailhog-data
       - ../..:/project
       - ../..:/wp-core/wp-content/plugins/mailpoet
-      - ../../../mailpoet-premium:/wp-core/wp-content/plugins/mailpoet-premium
+      - ../../../mailpoet-premium:/project/mailpoet-premium
       - ./codeception/docker-entrypoint.sh:/docker-entrypoint.sh
       - ../../../dev/php.ini:/usr/local/etc/php/conf.d/php_user.ini
       - ../../../dev/xdebug.ini:/usr/local/etc/php/conf.d/xdebug.ini
@@ -39,7 +39,7 @@ services:
       - mailhog-data:/mailhog-data
       - ../..:/project
       - ../..:/wp-core/wp-content/plugins/mailpoet
-      - ../../../mailpoet-premium:/wp-core/wp-content/plugins/mailpoet-premium
+      - ../../../mailpoet-premium:/project/mailpoet-premium
       - ./codeception/docker-entrypoint.sh:/docker-entrypoint.sh
       - ../../../dev/php.ini:/usr/local/etc/php/conf.d/php_user.ini
       - ../../../dev/xdebug.ini:/usr/local/etc/php/conf.d/xdebug.ini
@@ -77,7 +77,7 @@ services:
     volumes:
       - wp-core:/var/www/html
       - ../..:/var/www/html/wp-content/plugins/mailpoet
-      - ../../../mailpoet-premium:/wp-core/wp-content/plugins/mailpoet-premium
+      - ../../../mailpoet-premium:/project/mailpoet-premium
     tmpfs:
       - /var/www/html/wp-content/uploads/mailpoet/
     ports: