[BUGFIX] Mark guzzlehttp/guzzle >= 6.5.0 as conflict

Due to the INTL/ICU bug, which we
have seen on various places, Guzzle, which
does not cover our edge cases yet, ran
in the same issue as our Core versions earlier
in 2019.

See
https://github.com/guzzle/guzzle/issues/2448
https://github.com/guzzle/guzzle/pull/2454

For the time being, lets mark guzzle as
incompatible until Guzzle has solved the issue
and released a new version, so we can loosen
the conflict constraint.

Related: #87953
Resolves: #89904
Releases: master, 9.5, 8.7
Change-Id: If64fb9472d046f020c850cd0551beeaf78796b60
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62606


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>