Update LibGit2Sharp 0.28.0 -> 0.31.0 causes crash on ubuntu

[AArnott]

I'm blocked in updating to the latest libgit2sharp because of an apparently new failure that causes process crashes.

From this test run:

The active test run was aborted. Reason: Test host process crashed : free(): invalid pointer

[bording]

CI runs the test suite here on on Ubuntu 20.04, 22.04, and 24.04 just fine, so I'm going to need some sort of repro that demonstrates the problem.

[AArnott]

That's fair. I ran it twice more and it didn't repro.