[TASK] Upgrade to composer/composer ^2.6.5

> composer req --dev composer/composer ^2.6.5

Raised development dependencies, since v2.6.4 fixes
CVE-2023-43655 which concerns "web-accessible server
where the composer.phar can be executed as a php file"
(which is not a security issue for TYPO3 in this case).

Resolves: #102128
Releases: main, 12.4, 11.5
Change-Id: I3fd478fa7cee2c875b560f79cab94cb889d2b73a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81386
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: Oliver Hader <oliver.hader@typo3.org>

composer.json

@@ -108,7 +108,7 @@
 		"codeception/module-cli": "^2.0.1",
 		"codeception/module-filesystem": "^3.0.0",
 		"codeception/module-webdriver": "^4.0.0",
-		"composer/composer": "^2.5.5",
+		"composer/composer": "^2.6.5",
 		"friendsofphp/php-cs-fixer": "^3.26.1",
 		"friendsoftypo3/phpstan-typo3": "^0.9.0",
 		"php-webdriver/webdriver": "^1.14.0",