Update circleci/mysql 5.7.27 and 8.0 to cimg/mysql

MAILPOET-4103

.circleci/config.yml

@@ -104,8 +104,8 @@ executors:
     <<: *default_job_config
     docker:
       - image: mailpoet/wordpress:8.1_20220309.1
-      - image: circleci/mysql:8.0-ram
-        command: [--default-authentication-plugin=mysql_native_password]
+      - image: cimg/mysql:8.0
+        command: --default-authentication-plugin=mysql_native_password --character-set-server=utf8mb4 --collation-server=utf8mb4_unicode_520_ci
 
 jobs:
   build:

mailpoet/tests/docker/docker-compose.yml

@@ -58,7 +58,7 @@ services:
           - test.local
 
   mysql:
-    image: circleci/mysql:${MYSQL_IMAGE_VERSION:-5.7.27-ram}
+    image: cimg/mysql:${MYSQL_IMAGE_VERSION:-5.7.36}
     # Command used for MySQL 8+ because it needs default-authentication-plugin
     # parameter and there needs to be some fallback for other MySQL versions.
     # --verbose can be changed to any other useless parameter