Merge remote-tracking branch 'upstream/2.15.x' into 1.x

* upstream/2.15.x:
  Make property private in final class
  Update actions/checkout action to v3
  Update actions/cache action to v3
  Enable installation of PHPCS plugins that setup CS rulesets
  Add renovate.json
  Remove codelicia/xulieta as a dev dependencies
  Raise awareness of current Russia-Ukraine situation, targeting Russian 🇷🇺  readers

Author: nicolas-grekas

.github/workflows/phpunit.yml

@@ -30,7 +30,7 @@ jobs:
 
     steps:
       - name: "Checkout"
-        uses: "actions/checkout@v2"
+        uses: "actions/checkout@v3"
 
       - name: "Install PHP"
         uses: "shivammathur/setup-php@v2"
@@ -41,7 +41,7 @@ jobs:
           tools: composer:v2, cs2pr
 
       - name: "Cache dependencies"
-        uses: "actions/cache@v2"
+        uses: "actions/cache@v3"
         with:
           path: |
             ~/.composer/cache

src/ProxyManager/Inflector/ClassNameInflector.php

@@ -14,7 +14,7 @@
 
 final class ClassNameInflector implements ClassNameInflectorInterface
 {
-    protected $proxyNamespace;
+    private $proxyNamespace;
     /** @var int @TODO annotation still needed for phpstan to understand this */
     private $proxyMarkerLength;
     private $proxyMarker;