[TOOLS][TESTS] Make tests run as www-data

docker/testing/Dockerfile

@@ -3,6 +3,6 @@ FROM gsocial/php
 WORKDIR /var/www/social
 
 RUN apk update \
-    && apk add --no-cache $PHPIZE_DEPS \
+    && apk add --no-cache $PHPIZE_DEPS runuser \
     && pecl install xdebug \
     && docker-php-ext-enable xdebug

docker/testing/coverage.sh

@@ -4,7 +4,7 @@ cd /var/www/social || exit 65
 
 yes yes | php bin/console doctrine:fixtures:load || exit 65
 
-if bin/phpunit --coverage-html .test_coverage_report; then
+if runuser -u www-data -- bin/phpunit --coverage-html .test_coverage_report; then
     exit 64
 else
     exit 65