Merge branch '5.4' into 6.0

* 5.4:
  [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

Tests/Dumper/ServerDumperTest.php

@@ -39,6 +39,10 @@ public function testDumpForwardsToWrappedDumperWhenServerIsUnavailable()
 
     public function testDump()
     {
+        if ('True' === getenv('APPVEYOR')) {
+            $this->markTestSkipped('Skip transient test on AppVeyor');
+        }
+
         $wrappedDumper = $this->createMock(DataDumperInterface::class);
         $wrappedDumper->expects($this->never())->method('dump'); // test wrapped dumper is not used