Failed to ping DB , dial tcp connect: connection refused

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Failed to ping DB , dial tcp connect: connection refused

Steps to reproduce
How can we reproduce the issue (what version are you using?)
while installing 7.10.3 mattermost version
I used such commands -

tar -xvzf mattermost*.gz
sudo mv mattermost /opt
sudo mkdir /opt/mattermost/data
sudo useradd --system --user-group mattermost
sudo chown -R mattermost:mattermost /opt/mattermost
sudo chmod -R g+w /opt/mattermost
sudo chmod -R g+w /opt/mattermost

after this I installed My SQL server using these commands
sudo apt update
sudo apt install mysql-server
sudo systemctl start mysql.service
also configured the MySQL with my desired password

sudo mysql

>> ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'pass';


finally, I started creating, configuring mattermost db 

sudo nano /opt/mattermost/config/config.json
and changed this 
"DriverName": "mysql",
"DataSource": "root:pass@tcp(localhost:3306)/mattermost?charset=utf8mb4,utf8&writeTimeout=30s"

For creating
mysql -u root -p

>> create database mattermost;

after this I tried to test if mattermost was working or not by using this command
cd /opt/mattermost
sudo -u mattermost bin/mattermost

**Expected behavior**
while testing the mattermost should work on the given port number  without any error

**Observed behavior**
while launching the server I got stuck with an error

ubuntu@ayush:/opt/mattermost$ cd /opt/mattermost
sudo -u mattermost bin/mattermost
{"timestamp":"2023-06-26 18:35:56.897 Z","level":"info","msg":"Server is initializing...","caller":"platform/service.go:165","go_version":"go1.19.5"}
{"timestamp":"2023-06-26 18:35:56.898 Z","level":"info","msg":"Pinging SQL","caller":"sqlstore/store.go:242","database":"master","dataSource":"**:**@tcp(localhost:3306)/mattermost?writeTimeout=30s&charset=utf8mb4%2Cutf8"}
{"timestamp":"2023-06-26 18:35:56.900 Z","level":"error","msg":"Failed to ping DB","caller":"sqlstore/store.go:252","error":"dial tcp connect: connection refused","retrying in seconds":10}