Mailer templates do not get reloaded in dev mode

### Description

Mail templates are not reloaded in dev mode.

### Gitea Version

1.16+

### Can you reproduce the bug on the Gitea demo site?

No

### Log Gist

_No response_

### Screenshots

_No response_

### Git Version

_No response_

### Operating System

_No response_

### How are you running Gitea?

N/A

### Database

_No response_