Merge branch '6.1' into 6.2

* 6.1:
  [HttpClient] Fix computing retry delay when using RetryableHttpClient
  [Uid] Fix validating UUID variant bits
  [Validator][UID] Stop to first ULID format violation
  [Bridge] Fix mkdir() race condition in ProxyCacheWarmer
  [Cache] update readme
  Bug #42343 [Security] Fix valid remember-me token exposure to the second consequent request
  Prevent exception if request stack is empty
  Psr18Client ignore invalid HTTP headers
  skip a transient test on AppVeyor

Author: nicolas-grekas

DataCollector/RequestDataCollector.php

@@ -107,7 +107,7 @@ public function collect(Request $request, Response $response, \Throwable $except
             'session_metadata' => $sessionMetadata,
             'session_attributes' => $sessionAttributes,
             'session_usages' => array_values($this->sessionUsages),
-            'stateless_check' => $this->requestStack?->getMainRequest()->attributes->get('_stateless') ?? false,
+            'stateless_check' => $this->requestStack?->getMainRequest()?->attributes->get('_stateless') ?? false,
             'flashes' => $flashes,
             'path_info' => $request->getPathInfo(),
             'controller' => 'n/a',

Tests/DataCollector/RequestDataCollectorTest.php

@@ -312,6 +312,15 @@ public function testStatelessCheck()
         $collector->lateCollect();
 
         $this->assertTrue($collector->getStatelessCheck());
+
+        $requestStack = new RequestStack();
+        $request = $this->createRequest();
+
+        $collector = new RequestDataCollector($requestStack);
+        $collector->collect($request, $response = $this->createResponse());
+        $collector->lateCollect();
+
+        $this->assertFalse($collector->getStatelessCheck());
     }
 
     public function testItHidesPassword()