Merge branch '6.4' into 7.0

* 6.4:
  [Translation] Improve tests coverage
  [Routing] Add redirection.io as sponsor of versions 6.4/7.0/7.1
  don't check parameter values if they are not set
  [HttpClient] Add Innovative Web AG (i-web) as sponsor of version 6.4/7.0
  [Serializer] Fix normalization relying on allowed attributes only
  Minor @var doc update
  [Translation] Remove `@internal` from abstract testcases
  [VarExporter] Work around php/php-src#12695 for lazy objects, fixing nullsafe-related behavior
  [Validator] Add missing translations for Bulgarian #51931
  [VarExporter] Fix serializing objects that implement __sleep() and that are made lazy
  fix typo
  Document BC break with $secret parameter introduction
  Bump Symfony version to 6.4.0
  Update VERSION for 6.4.0-RC2
  Update CHANGELOG for 6.4.0-RC2
  [String] Fix Inflector for 'icon'
  [Validator] Made tests forward-compatible with ICU 72.1

Author: nicolas-grekas

README.md

@@ -3,6 +3,18 @@ HttpClient component
 
 The HttpClient component provides powerful methods to fetch HTTP resources synchronously or asynchronously.
 
+Sponsor
+-------
+
+The HttpClient component for Symfony 7.0 is [backed][1] by [Innovative Web AG][2].
+
+Innovative Web AG (i-web) is a specialist for web, applications and the
+digitalisation of the public sector based in Switzerland. With their i-CMS,
+public authorities and institutions implement modern websites and eGovernment
+portals and offer user-friendly eServices for residents and companies.
+
+Help Symfony by [sponsoring][3] its development!
+
 Resources
 ---------
 
@@ -11,3 +23,7 @@ Resources
  * [Report issues](https://github.com/symfony/symfony/issues) and
    [send Pull Requests](https://github.com/symfony/symfony/pulls)
    in the [main Symfony repository](https://github.com/symfony/symfony)
+
+[1]: https://symfony.com/backers
+[2]: https://www.i-web.ch
+[3]: https://symfony.com/sponsor