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

src/Wallabag/CoreBundle/Entity/Entry.php

@@ -682,6 +682,19 @@ class Entry
         return $this->tags;
     }
 
+    /**
+     * Only used during tests.
+     */
+    public function getTagsLabel(): array
+    {
+        $tags = [];
+        foreach ($this->tags as $tag) {
+            $tags[] = $tag->getLabel();
+        }
+
+        return $tags;
+    }
+
     /**
      * @VirtualProperty
      * @SerializedName("tags")