mysql: use collation instead of charset (#9156)

- use charset would issue additional 'SET NAMES <VALUE>' queries, set
collation would be better. see: https://github.com/go-sql-driver/mysql#charset

pkg/services/sqlstore/sqlstore.go

@@ -114,7 +114,7 @@ func getEngine() (*xorm.Engine, error) {
 			protocol = "unix"
 		}
 
-		cnnstr = fmt.Sprintf("%s:%s@%s(%s)/%s?charset=utf8mb4&allowNativePasswords=true",
+		cnnstr = fmt.Sprintf("%s:%s@%s(%s)/%s?collation=utf8mb4_unicode_ci&allowNativePasswords=true",
 			DbCfg.User, DbCfg.Pwd, protocol, DbCfg.Host, DbCfg.Name)
 
 		if DbCfg.SslMode == "true" || DbCfg.SslMode == "skip-verify" {