Use getenv() function instead of $_ENV global variable. (#1887)

* ComposerTask: update code & doc #1163

* refactor(PropertyTask): Use getenv() function instead of $_ENV global variable.

The PropertyTask's "environment" attribute fails to work as expected in some systems, sometimes $_ENV is an empty array.
This behavior is system-dependent and determined by the "variables_order" directive in php.ini.

To fix this I replaced $_ENV by getenv() function, as this ensures a consistent behaviour.

* https://www.php.net/manual/en/ini.core.php#ini.variables-order
* https://stackoverflow.com/questions/8798294/getenv-vs-env-in-php

src/Phing/Task/System/PropertyTask.php

@@ -412,7 +412,7 @@ protected function loadEnvironment(string $prefix)
             $prefix .= '.';
         }
         $this->log("Loading Environment {$prefix}", Project::MSG_VERBOSE);
-        foreach ($_ENV as $key => $value) {
+        foreach (getenv() as $key => $value) {
             $props->setProperty($prefix . '.' . $key, $value);
         }
         $this->addProperties($props);

tests/Phing/Test/Task/System/PropertyTaskTest.php

@@ -38,8 +38,9 @@ public function setUp(): void
 
     public function test1(): void
     {
-        // should get no output at all
-        $this->expectOutputAndError('test1', '', '');
+        putenv('MESSAGE=foo bar baz');
+        $this->executeTarget(__FUNCTION__);
+        $this->assertPropertyEquals('testenv.MESSAGE', 'foo bar baz');
     }
 
     public function test2(): void