Merge branch '4.4' into 5.0

* 4.4:
  [DependencyInjection] Fix binding tagged services to containers
  [ProxyManager] fix generating proxies for root-namespaced classes
  [DI] skip looking for config class when the extension class is anonymous
  Fix typo
  Docs - Update debug section of UPGRADE guides for 4.4 and 5.0 versions.
  [Dotenv] FIX missing getenv
  [HttpFoundation] fix pdo session handler for sqlsrv
  [HttpClient][Psr18Client] Remove Psr18ExceptionTrait
  [HttpKernel] ignore failuresgenerated by opcache.restrict_api

Author: nicolas-grekas

Dotenv.php

@@ -458,7 +458,7 @@ private function resolveVariables(string $value, array $loadedVars): string
             } elseif (isset($this->values[$name])) {
                 $value = $this->values[$name];
             } else {
-                $value = '';
+                $value = (string) getenv($name);
             }
 
             if ('' === $value && isset($matches['default_value']) && '' !== $matches['default_value']) {

Tests/DotenvTest.php

@@ -443,6 +443,17 @@ public function testGetVariablesValueFromEnvFirst()
         }
     }
 
+    public function testGetVariablesValueFromGetenv()
+    {
+        putenv('Foo=Bar');
+
+        $dotenv = new Dotenv(true);
+        $values = $dotenv->parse('Foo=${Foo}');
+        $this->assertSame('Bar', $values['Foo']);
+
+        putenv('Foo');
+    }
+
     public function testNoDeprecationWarning()
     {
         $dotenv = new Dotenv(true);