Changelog should be generated before tagging latest version

[strongoier]

In the release of v1.1.3, the workflow generates an incomplete changelog (https://github.com/taichi-dev/taichi/actions/runs/3087352313/jobs/4993540670):

Highlights: Full changelog: - [bug] [gui] Fix a bug of drawing mesh instacing that cpu/cuda objects have an offset when copying to vulkan object (#6028) (by **Mocki**)

It seems that the latest version has been tagged before changelog generation. However, the setting looks correct: https://github.com/taichi-dev/taichi/blob/02822e70d1100b1adca9bc3796f7cee9408053fa/.github/workflows/release.yml#L454-L472

There must be something wrong. If we don't fix it, we will have to locally generate the changelog and manually paste it immediately after each release.