Bump up the minimum required MySQL version (#25465)

MySQL 5.7 is at end of life.

https://mattermost.atlassian.net/browse/MM-55589

```release-note
We bump up minimum MySQL version to be 8.0.0
```


Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Ibrahim Serdar Acikgoz <serdaracikgoz86@gmail.com>

.github/workflows/server-ci-template.yml

@@ -285,7 +285,7 @@ jobs:
     uses: ./.github/workflows/server-test-template.yml
     with:
       name: MySQL
-      datasource: mmuser:mostest@tcp(mysql:3306)/mattermost_test?charset=utf8mb4,utf8&multiStatements=true&maxAllowedPacket=4194304
+      datasource: mmuser:mostest@tcp(mysql:3306)/mattermost_test?charset=utf8mb4&multiStatements=true&maxAllowedPacket=4194304
       drivername: mysql
       logsartifact: mysql-server-test-logs
     secrets: inherit