Release v3.4.26

[fabpot]

Changelog (since v3.4.25...v3.4.26)

• bug [HttpFoundation] Make MimeTypeExtensionGuesser case insensitive #31084 [HttpFoundation] Make MimeTypeExtensionGuesser case insensitive (@vermeirentony)
• bug Revert "bug #30423 [Security] Rework firewall's access denied rule (dimabory)" #31142 Revert "bug [Security] Rework firewall's access denied rule #30423 [Security] Rework firewall's access denied rule (dimabory)" (@chalasr)
• security #cve-2019-10910 [DI] Check service IDs are valid (@nicolas-grekas)
• security #cve-2019-10909 [FrameworkBundle][Form] Fix XSS issues in the form theme of the PHP templating engine (@stof)
• security #cve-2019-10912 [Cache][PHPUnit Bridge] Prevent destructors with side-effects from being unserialized (@nicolas-grekas)
• security #cve-2019-10911 [Security] Add a separator in the remember me cookie hash (@pborreli)
• security #cve-2019-10913 [HttpFoundation] reject invalid method override (@nicolas-grekas)