CI: 'seen' minus a few passes tests, eh, almost

It is sad that the tip of 'seen' rarely passes all tests these days.

I excluded a few topics (chosen primarily by prejudice after looking at which tests failed earlier, without locating exactly where and why they fail) from 'seen' and the exclusion of them seems to have made 'seen' finally pass the tests, eh, almost [*1*].

82b1e47 is such a "reduced" 'seen' branch, and the CI run for it can be found here:

  https://github.com/git/git/actions/runs/876448385

Excluded are:

  ab/fsck-unexpected-type
  hn/reftable
  hn/refs-errno-cleanup
  zh/ref-filter-raw-data

Any of these may not be broken by themselves, and it could be that the tests may still pass even if one or some of them are merged on top of 82b1e47 and the problem may manifest only when two or more of these topics in certain combinations are merged to 'seen'.

The CI run for 'seen' with all these four topics merged back can be found here:

  https://github.com/git/git/actions/runs/876534959

[Footnote]

*1* Except for "git repack" segfaults only in one of the tests:

  https://github.com/git/git/runs/2669668815?check_suite_focus=true#step:5:2846