Git index version 3 support

[sebastianst]

Using git python to add files to an index fails at an index head assertion if the local repo is being otherwise worked on with git 2.46.0:

GitPython/git/index/fun.py

Lines 209 to 210 in cfadd9e

	# TODO: Handle version 3: extended data, see read-cache.c.
	assert version in (1, 2)

Is it planned to add support for version 3 soon?

I couldn't find any ticket tracking this, so apologies if this is a duplicate.

[Byron]

There is no plan to add support for extended index flag in V3, even though it would probably be quite easy to add if someone wanted to contribute support for it.

Generally, I probably wouldn't trust the index implementation as it is here and if possible, repo.git might be able to do the same with a decent amount of convenience.