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:

taichi/.github/workflows/release.yml

Lines 454 to 472 in 02822e7

	- name: Generate Changelog
	id: changelog
	run: |
	pip3 install gitpython
	content=$(python3 misc/make_changelog.py)
	echo $content
	# Escape multiline strings:
	# https://renehernandez.io/snippets/multiline-strings-as-a-job-output-in-github-actions/
	content="${content//'%'/'%25'}"
	content="${content//$'\n'/'%0A'}"
	content="${content//$'\r'/'%0D'}"
	echo "::set-output name=content::$content"
	- name: Create tag
	run: |
	git config user.email "[email protected]"
	git config user.name "Taichi Gardener"
	git tag -a ${RELEASE_VERSION} -m "Release ${RELEASE_VERSION}"
	git push origin --tags

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.