chore: update codebase to php8.1 (#3827)

* chore: set minimum php version to 8.1

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* chore: update codebase to php8.1

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* Apply fixes from StyleCI

* chore: update workflow php version

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* fix: caught errors

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* fix: more caught errors

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* fix: phpstan caught errors

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* Apply fixes from StyleCI

* fix: test-caught errors

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* fix: test-caught errors

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* fix: test-caught errors

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* fix: introduce `Flarum\Locale\TranslatorInterface`

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* Apply fixes from StyleCI

* chore: remove mixin

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* fix: test-caught errors

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

* fix: one last error

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>

---------

Signed-off-by: Sami Mazouz <sychocouldy@gmail.com>
Co-authored-by: StyleCI Bot <bot@styleci.io>

.github/workflows/REUSABLE_backend.yml

@@ -25,7 +25,7 @@ on:
         description: Versions of PHP to test with. Should be array of strings encoded as JSON array
         type: string
         required: false
-        default: '["7.3", "7.4", "8.0", "8.1", "8.2"]'
+        default: '["8.1", "8.2"]'
 
       php_extensions:
         description: PHP extensions to install.