fix: storage(minio): prevent io.Reader close (#8541)

Fixes #8529, reverts #8527.

I was able to reproduce the problem in a test:
- it triggered only when the reader was an io.Reader
- and the size was provided (-1 takes another code path in minio)

287b1f21e1 should fail when running:
```
docker run --rm -e MINIO_DOMAIN=minio -e MINIO_ROOT_USER=123456 -e MINIO_ROOT_PASSWORD=12345678 -p 9000:9000  data.forgejo.org/oci/bitnami/minio:2024.8.17
```

and

```
TEST_MINIO_ENDPOINT=localhost:9000  go test -v -run ^TestMinioStorageIterator$ ./modules/storage
```

### Tests

- I added test coverage for Go changes...
  - [x] in their respective `*_test.go` for unit tests.
  - [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.

### Documentation

- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.

### Release notes

- [x] I do not want this change to show in the release notes.
- [ ] I want the title to show in the release notes with a link to this pull request.
- [ ] I want the content of the `release-notes/<pull request number>.md` to be be used for the release notes instead of the title.

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8541
Reviewed-by: Michael Kriese <michael.kriese@gmx.de>
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: oliverpool <git@olivier.pfad.fr>
Co-committed-by: oliverpool <git@olivier.pfad.fr>

modules/storage/minio.go

@@ -209,7 +209,7 @@ func (m *MinioStorage) Save(path string, r io.Reader, size int64) (int64, error)
 		m.ctx,
 		m.bucket,
 		m.buildMinioPath(path),
-		r,
+		io.NopCloser(r), // prevent minio from closing the reader
 		size,
 		minio.PutObjectOptions{
 			ContentType: "application/octet-stream",