Codespace: Also ensure composer deps like phpunit are usable in devcontainer

.devcontainer/postCreateCommand.sh

@@ -1,5 +1,8 @@
 #!/bin/sh
 
+export PATH="$PATH:$HOME/.composer/vendor/bin"
 composer install --no-dev --optimize-autoloader
+
 sudo chmod a+x "$(pwd)" && sudo rm -rf /var/www/html && sudo ln -s "$(pwd)" /var/www/html
+
 npm install --global nyc