chore(codespace): install stuff for PHP unit testing

.devcontainer/postCreateCommand.sh

@@ -7,6 +7,10 @@ echo 'export PATH="$PATH:$PWD/vendor/bin"' >> ~/.bashrc
 ln -s ./conf.sample.php cfg/conf.php
 composer install --no-dev --optimize-autoloader
 
+# for PHP unit testing
+composer require google/cloud-storage
+composer install --optimize-autoloader
+
 sudo chmod a+x "$(pwd)" && sudo rm -rf /var/www/html && sudo ln -s "$(pwd)" /var/www/html
 
 npm install --global nyc