fix: do not mix urfave v2 with urfave v3 (#8168)

[Spotted](https://codeberg.org/forgejo/forgejo/pulls/8137#issuecomment-5079471) by @nilsph

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### Tests

- I added test coverage for Go changes...
  - [ ] in their respective `*_test.go` for unit tests.
  - [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I added test coverage for JavaScript changes...
  - [ ] in `web_src/js/*.test.js` if it can be unit tested.
  - [ ] in `tests/e2e/*.test.e2e.js` if it requires interactions with a live Forgejo server (see also the [developer guide for JavaScript testing](https://codeberg.org/forgejo/forgejo/src/branch/forgejo/tests/e2e/README.md#end-to-end-tests)).

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
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### Release notes

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- [ ] I want the title to show in the release notes with a link to this pull request.
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Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8168
Reviewed-by: Otto <otto@codeberg.org>
Co-authored-by: Earl Warren <contact@earl-warren.org>
Co-committed-by: Earl Warren <contact@earl-warren.org>

main.go

@@ -21,7 +21,7 @@ import (
 	_ "forgejo.org/modules/markup/markdown"
 	_ "forgejo.org/modules/markup/orgmode"
 
-	"github.com/urfave/cli/v2"
+	"github.com/urfave/cli/v3"
 )
 
 // these flags will be set by the build flags