fmt bumps last modified time even when no changes were made

[d-honeybadger]

Describe the bug
swag fmt touches go files in the directory regardless of whether any changes were made in each of those files.
This minor detail comes to bite anyone who uses live-update build tools (e.g. observed with Tilt): if you want to automatically run swag fmt on changes to go files, this bumps lastmodified time, which then triggers another swag fmt, which ...

To Reproduce

1. run swag fmt to make sure all comments are properly formatted
2. note the last modified time of the files:

> ls -l
...
-rw-------  1 d-honeybadger d-honeybadger 17928 Jul 27 15:33 main.go

3. Without making any changes to main.go, run swag fmt again
4. Note that the last modified time got updated, even though this time no formatting changes were necessary:

> ls -l
...
-rw-------  1 d-honeybadger d-honeybadger 17928 Jul 27 15:35 main.go

Expected behavior
When no changes are made to a file, swag fmt should leave it as-is, without replacing/touching

Your swag version
e.g. 1.8.12

Your go version
e.g. 1.20.5

Desktop (please complete the following information):

• OS: Ubuntu
• Version: 20.04