gh-620: Explicitly include InstalledVersions.php and installed.php in PHAR

The autoloadmap includes a mapping `Composer\InstalledVersions` but as
of explicitly including `src` this file is no longer included.

This commit explicitly adds both `vendor/composer/InstalledVersions.php`
and `vendor/composer/installed.php` to ensure that the previous behavior
is preserved and WARNINGS are not issued when other packages use
`InstalledVersions::getVersion(// ...)`.

Author: dantleech

CHANGELOG.md

@@ -8,6 +8,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 For a full diff see [`2.16.0...main`][2.16.0...main].
 
+### Fixed
+
+- Explicitly included `vendor/composer/installed.php` and `vendor/composer/InstalledVersions.php` when building PHAR ([#621]), by [@dantleech]
+
 ## [`2.16.0`][2.16.0]
 
 For a full diff see [`2.15.1...2.16.0`][2.15.1...2.16.0].
@@ -360,6 +364,7 @@ For a full diff see [`7afa59c...1.0.0`][7afa59c...1.0.0].
 [#598]: https://github.com/ergebnis/phpunit-slow-test-detector/pull/598
 [#604]: https://github.com/ergebnis/phpunit-slow-test-detector/pull/604
 
+[@dantleech]: https://github.com/dantleech
 [@HypeMC]: https://github.com/HypeMC
 [@localheinz]: https://github.com/localheinz
 [@mvorisek]: https://github.com/mvorisek

box.json

@@ -9,7 +9,9 @@
     "src/"
   ],
   "files": [
-    "manifest.xml"
+    "manifest.xml",
+    "vendor/composer/installed.php",
+    "vendor/composer/InstalledVersions.php"
   ],
   "git": "git",
   "main": "phar/phpunit-slow-test-detector.php",