* 5.1: (25 commits)
  stop using the deprecated at() PHPUnit matcher
  fix lowest allowed version of the HTTP client contracts
  fix lowest allowed version for the PHPUnit bridge
  fix merge
  fix merge
  drop logger mock in favor of using the BufferingLogger
  catch ValueError thrown on PHP 8
  [Yaml Parser] Fix edge cases when parsing multiple documents
  fix parsing comments not prefixed by a space
  [Translator] Make sure a null locale is handled properly
  deal with errors being thrown on PHP 8
  loadRoutes shoud receive RoutingPhpFileLoader
  [Cache] Allow cache tags to be objects implementing __toString()
  [HttpKernel] Do not override max_redirects option in HttpClientKernel
  Log notice when no entry point is configured
  remove superfluous cast
  [HttpClient] Support for CURLOPT_LOCALPORT.
  Upgrade PHPUnit to 8.5 (php 7.2) and 9.3 (php >= 7.3).
  Fixed exception message formatting
  [FrameworkBundle] Fix error in xsd which prevent to register more than one metadata
  ...

This PR was squashed before being merged into the 4.4 branch.

Discussion
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[Translator] Optional Intl dependency

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix #38279
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!-- required for new features -->
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i decided to cast $locale at construct, given its property is documented to be string

Commits
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a2eb263 [Translator] Optional Intl dependency