Update composer Docker tag to v2.6.6

This MR contains the following updates:

Package	Type	Update	Change
composer	image	patch	2.6.5 -> 2.6.6

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.gitlab-ci.yml

@@ -7,7 +7,7 @@ variables:
 
 PHPstan:
   stage: test
-  image: composer:2.6.5
+  image: composer:2.6.6
   before_script:
     - composer install --ignore-platform-reqs
   script:
@@ -77,7 +77,7 @@ Webpack:
 
 Composer:
   stage: build
-  image: composer:2.6.5
+  image: composer:2.6.6
   script:
     - apk add php-cli composer php-gd php-ctype php-xml php-simplexml php-xmlwriter php-tokenizer php-session php-dom php-mysqli php-pdo_mysql
     - composer install --optimize-autoloader