[CI] Install payum/paypal-express-checkout-nvp during the workflow

.github/workflows/build.yml

@@ -57,6 +57,12 @@ jobs:
                     composer global require --no-progress --no-scripts --no-plugins "symfony/flex:^2.4"
                     composer config extra.symfony.require "${{ matrix.symfony }}"
 
+            # This dependency in Sylius has been shifted to dev dependencies: https://github.com/Sylius/Sylius/pull/15485
+            -
+                name: Add Paypal Express Checkout dev dependency
+                run: |
+                    composer require --dev --no-update --no-progress --no-scripts --no-plugins "payum/paypal-express-checkout-nvp:^1.7.3"
+
             -
                 name: Setup Node
                 uses: actions/setup-node@v2