Merge pull request libgit2#4475 from pks-t/pks/v0.26.1-backports

v0.26.3 backports

Merge pull request libgit2#4572 from pks-t/pks/index-secfixes

Security fixes for reading index v4

Merge pull request libgit2#4568 from pks-t/pks/zlib-update-0.26

deps: upgrade embedded zlib to version 1.2.11

Merge pull request libgit2#4545 from libgit2/ethomson/checkout_filemode

Respect core.filemode in checkout

Merge pull request libgit2#4533 from pks-t/pks/v0.27.0-rc1

v0.27.0-rc1: version bump

CHANGELOG: document git_filter_init and GIT_FILTER_INIT

CHANGELOG: document git_filter_init and GIT_FILTER_INIT

Merge pull request libgit2#4262 from libgit2/ethomson/bump-v26

Update version number to 0.26

Merge pull request libgit2#4076 from libgit2/cmn/sec-update-25

security updates for v0.25

Merge pull request libgit2#4075 from libgit2/cmn/sec-update-24

Security updates for v0.24