Ping server integration test dependencies to phpunit 8

Signed-off-by: Julius Härtl <jus@bitgrid.net>

.github/workflows/integration.yml

@@ -54,6 +54,7 @@ jobs:
           auth_header="$(git config --local --get http.https://github.com/.extraheader)"
           git submodule sync --recursive
           git -c "http.extraheader=$auth_header" -c protocol.version=2 submodule update --init --force --recursive --depth=1
+          cd build/integration && composer require --dev phpunit/phpunit:~8
 
       - name: Checkout app
         uses: actions/checkout@v3