naoki kuroda

I upgraded Go version to 1.19 in go.mod. I executed `go mod tidy -go=1.19`.

fix: logging error

2

## Related Issue - Info about Issue or bug Closes: #1588 #### Describe the changes you've made A clear and concise description of what you have done to successfully close...

### Is there an existing issue for this? - [X] I have searched the existing issues ### Current behavior Some logs are not printed where they should be. ### Steps...

**What this PR does / why we need it**: This PR removes an validation check in the Validate method of the NotificationMention struct. This contradicts our documentation( https://pipecd.dev/docs-v0.48.x/user-guide/configuration-reference/#notificationmention ), which...