doc: use the correct release tarball, which includes generated content

[nilason]

With the 8.4.2 release, the wrong tarball ended up on the server. One that is missing the generated files from this part:

grass/.github/workflows/create_release_draft.yml

Lines 50 to 61 in a0b6166

	- name: Generate Git derived data files
	run: |
	echo "Generate VERSION_GIT file:"
	./utils/generate_version_git_file.sh
	cat include/VERSION_GIT
	echo "Generate GENERATE_LAST_COMMIT_FILE:"
	python utils/generate_last_commit_file.py .
	cat core_modules_with_last_commit.json
	echo "Create core modules patch file:"
	git add core_modules_with_last_commit.json
	git diff --cached > \
	"${OUT_DIR}/core_modules_with_last_commit.patch"

(But for 8.4.2. this is too late, we cannot/mustn't replace the tarball now, that will lead to problems. )

[wenzeslaus]

Where do you think the md5sum should come from? Now it is locally generated, but there is one uploaded from the CI.

[nilason]

Where do you think the md5sum should come from? Now it is locally generated, but there is one uploaded from the CI.

I was thinking of adding an instruction of downloading the md5sum file and compare with a sum check on the downloaded tarball (a bit of a security check). After that it doesn't matter which file,

[nilason]

Now I added a instructions for download of *.sha256 file and running sha256sum with it. The *.sha256 file will, and should, be uploaded to server (along with the *.md5sum file).

Please test on a Linux machine.