[BUGFIX] Mark symfony/routing 4.2.7 as conflict

Symfony/routing 4.2.7 changed routing behaviour, breaking backwards
compatibility and our implementation. Reported at symfony:

https://github.com/symfony/symfony/pull/31107#issuecomment-484681404

Mark that version as conflict until the behaviour is fixed.

Composer commands:
 - composer update --lock

Resolves: #88171
Releases: master, 9.5
Change-Id: I6f2651a605c6339222626d37c307c04b8f0eadf8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60509


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Josef Glatz <josefglatz@gmail.com>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>