Don't rerun the tests when the PR description is edited (#6373)

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### Motivation and context
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Most of the time it's useless and just clogs up the build queue. When
it's useful (e.g. when removing "[Dependent]" from the title), it's easy
enough to retrigger the build manually by updating your branch.

Fixes #5921.

### How has this been tested?
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- [x] I submit my changes into the `develop` branch
- ~~[ ] I have added a description of my changes into the
[CHANGELOG](https://github.com/opencv/cvat/blob/develop/CHANGELOG.md)
file~~
- ~~[ ] I have updated the documentation accordingly~~
- ~~[ ] I have added tests to cover my changes~~
- ~~[ ] I have linked related issues (see [GitHub docs](

https://help.github.com/en/github/managing-your-work-on-github/linking-a-pull-request-to-an-issue#linking-a-pull-request-to-an-issue-using-a-keyword))~~
- ~~[ ] I have increased versions of npm packages if it is necessary

([cvat-canvas](https://github.com/opencv/cvat/tree/develop/cvat-canvas#versioning),

[cvat-core](https://github.com/opencv/cvat/tree/develop/cvat-core#versioning),

[cvat-data](https://github.com/opencv/cvat/tree/develop/cvat-data#versioning)
and

[cvat-ui](https://github.com/opencv/cvat/tree/develop/cvat-ui#versioning))~~

### License

- [x] I submit _my code changes_ under the same [MIT License](
https://github.com/opencv/cvat/blob/develop/LICENSE) that covers the
project.
  Feel free to contact the maintainers if that's a concern.

.github/workflows/main.yml

@@ -5,7 +5,7 @@ on:
       - 'master'
       - 'develop'
   pull_request:
-    types: [edited, ready_for_review, opened, synchronize, reopened]
+    types: [ready_for_review, opened, synchronize, reopened]
     paths-ignore:
       - 'site/**'
       - '**/*.md'