fix: Apply mysqld character set fix to Kubernetes deployment

This is a follow-up fix to openedx#819, where the corresponding change was
added to the mysqld invocation in the "tutor local" (that is,
docker-compose) deployment method, but omitted from its "tutor k8s"
equivalent.

changelog.d/20230824_104119_fghaas_utf8mb3_k8s.md

@@ -0,0 +1 @@
+- 💥[Bugfix] Apply "fix mysql crash after upgrade to Palm" from 16.1.0 to `tutor k8s` deployments, as well. Users previously running `tutor k8s` with `RUN_MYSQL: true`, with any version between 16.0.0 and 16.1.0 including, might have to fix their data manually. For users running `tutor local`, this change has no effect, as the underlying issue was already fixed in 16.1.0. For users running `tutor k8s` with `RUN_MYSQL: false`, this change is also a no-op. (by @fghaas)

tutor/templates/k8s/deployments.yml

@@ -392,7 +392,7 @@ spec:
       containers:
         - name: mysql
           image: {{ DOCKER_IMAGE_MYSQL }}
-          args: ["mysqld", "--character-set-server=utf8", "--collation-server=utf8_general_ci"]
+          args: ["mysqld", "--character-set-server=utf8mb3", "--collation-server=utf8mb3_general_ci"]
           env:
             - name: MYSQL_ROOT_PASSWORD
               value: "{{ MYSQL_ROOT_PASSWORD }}"