Add build test on PHP 8.0 & 8.1

Add `isTransactional` to `WallabagMigration` because PHP 8 behave differently with PDO transaction.
This is a workaround because we can't upgrade Doctrine Migration for now (upper versions have the fix).

- Build is now using Composer v2 (instead of v1)
- All actions have been updated to latest version
- Fix bug in PHP 8 were `$entry->getTags()` can't be properly used as a _traversable_ by `assertContains` during tests. Added a custom method `Entry::getTagsLabel()` which return a flatted tag array with only label
- Replace `assertNotRegExp` by `assertDoesNotMatchRegularExpression` because it was deprecated

.github/workflows/coding-standards.yml

@@ -20,15 +20,15 @@ jobs:
         uses: "shivammathur/setup-php@v2"
         with:
           coverage: "none"
-          php-version: "7.3"
-          tools: cs2pr, pecl, composer:v1
+          php-version: "7.4"
+          tools: cs2pr, pecl, composer:v2
           extensions: pdo, pdo_mysql, pdo_sqlite, pdo_pgsql, curl, imagick, pgsql, gd, tidy
           ini-values: "date.timezone=Europe/Paris"
         env:
           COMPOSER_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
       - name: "Install dependencies with Composer"
-        uses: "ramsey/composer-install@v1"
+        uses: "ramsey/composer-install@v2"
         with:
           composer-options: "--optimize-autoloader --prefer-dist"