Update changelog

CHANGELOG.md

@@ -1,3 +1,15 @@
+### [2.5.6] 2023-05-24
+
+  * BC Warning: Installers and `InstallationManager::getInstallPath` will now return `null` instead of an empty string for metapackages' paths. This may have adverse effects on plugin code using this expecting always a string but it is unlikely (#11455)
+  * Fixed metapackages showing their install path as the root package's path instead of empty (#11455)
+  * Fixed lock file verification on `install` to deal better with `replace`/`provide` (#11475)
+  * Fixed lock file having a more recent modification time than the vendor dir when `require` guesses the constraint after resolution (#11405)
+  * Fixed numeric default branches with a `v` prefix being treated as non-numeric ones and receiving an alias like e.g. dev-main would (e51d755a08)
+  * Fixed binary proxies not being transparent when included by another PHP process and returning a value (#11454)
+  * Fixed support for plugin classes being marked as `readonly` (#11404)
+  * Fixed `getmypid` being required as it is not always available (#11401)
+  * Fixed authentication issue when downloading several files from private Bitbucket in parallel (#11464)
+
 ### [2.5.5] 2023-03-21
 
   * Fixed basic auth failures resulting in infinite retry loop (#11320)
@@ -1708,6 +1720,7 @@
 
   * Initial release
 
+[2.5.6]: https://github.com/composer/composer/compare/2.5.5...2.5.6
 [2.5.5]: https://github.com/composer/composer/compare/2.5.4...2.5.5
 [2.5.4]: https://github.com/composer/composer/compare/2.5.3...2.5.4
 [2.5.3]: https://github.com/composer/composer/compare/2.5.2...2.5.3