[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
guzzle/guzzle#2448
guzzle/guzzle#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/+/62613
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>

composer.json

@@ -47,6 +47,7 @@
 		"ext-zlib": "TYPO3 uses zlib for amongst others output compression and un/packing t3x extension files"
 	},
 	"conflict": {
+		"guzzlehttp/guzzle": ">= 6.5.0",
 		"symfony/finder": "2.7.44 || 2.8.37 || 3.4.7 || 4.0.7",
 		"typo3/cms": "*",
 		"typo3fluid/fluid": "2.6.4 || 2.6.5"