Update dependency cimg/php to v8.1

Author: renovate[bot]

.circleci/config.yml

@@ -6,15 +6,15 @@ version: 2
 jobs:
   php74:
     docker:
-      - image: cimg/php:7.4
+      - image: cimg/php:8.1
     steps:
       - checkout
       - run: php -v
       - run: composer install --no-interaction
       - run: XDEBUG_MODE=coverage php vendor/bin/phpunit --coverage-text
   php80:
     docker:
-      - image: cimg/php:8.0
+      - image: cimg/php:8.1
     steps:
       - checkout
       - run: php -v