E2E/diff-colorized: add separate test for Windows

The colorized diff display on Windows is different from *nix systems.

This commit:
* Adds a test skip for the pre-existing test when the tests are run on Windows.
* Adds a separate test for the colorized diff display on Windows, which is skipped when running on *nix systems.

tests/end-to-end/testdox/diff-colorized-windows.phpt

@@ -0,0 +1,42 @@
+--TEST--
+TestDox: Diff; Colorized; Windows
+--SKIPIF--
+<?php declare(strict_types=1);
+if (stripos(\PHP_OS, 'WIN') !== 0) {
+    print 'skip: Colorized diff is different on *nix systems.';
+}
+--FILE--
+<?php declare(strict_types=1);
+$_SERVER['argv'][] = '--do-not-cache-result';
+$_SERVER['argv'][] = '--no-configuration';
+$_SERVER['argv'][] = '--testdox';
+$_SERVER['argv'][] = '--colors=always';
+$_SERVER['argv'][] = __DIR__ . '/_files/DiffTest.php';
+
+require_once __DIR__ . '/../../bootstrap.php';
+
+PHPUnit\TextUI\Command::main();
+--EXPECTF--
+PHPUnit %s by Sebastian Bergmann and contributors.
+
+Diff (PHPUnit\TestFixture\TestDox\Diff)
+ ✘ Something that does not work
+   ┐
+   ├ Failed asserting that two strings are equal.
+   ├ --- Expected                                
+   ├ +++ Actual                                  
+   ├ @@ @@                                       
+   ├  'foo\n                                     
+   ├ +baz\n                                      
+   ├  bar\n                                      
+   ├ -baz\n                                      
+   ├  '                                          
+   │
+   ╵ %stests%eend-to-end%etestdox%e_files%eDiffTest.php:%d
+   ┴
+
+Time: %s, Memory: %s
+
+
+FAILURES!
+Tests: 1, Assertions: 1, Failures: 1.

tests/end-to-end/testdox/diff-colorized.phpt

@@ -1,5 +1,10 @@
 --TEST--
-TestDox: Diff; Colorized
+TestDox: Diff; Colorized; *nix
+--SKIPIF--
+<?php declare(strict_types=1);
+if (stripos(\PHP_OS, 'WIN') === 0) {
+    print 'skip: Colorized diff is different on Windows.';
+}
 --FILE--
 <?php declare(strict_types=1);
 $_SERVER['argv'][] = '--do-not-cache-result';