why: Tell downstream users that the plugin now loads on pytest 9.1+, so
they can upgrade pytest without the session aborting before collection.
what:
- Add a Fixes entry under the 0.43.x unreleased block

…inary

why: vcs_gitconfig, set_vcs_gitconfig, vcs_hgconfig and set_vcs_hgconfig
only write a .gitconfig / .hgrc or set env vars -- they never invoke
git or hg. Guarding them on the binary made them skip when it was
absent. Because conftest.py's autouse `setup` fixture depends on
vcs_gitconfig, a host without git would skip the ENTIRE suite, including
svn- and hg-only tests that don't need git at all. The binary-invoking
fixtures (empty_git_repo, git_remote_repo, ...) keep their guards, so
tests that actually run a binary still skip correctly.

what:
- Remove _skip_if_git_missing() from vcs_gitconfig and set_vcs_gitconfig
- Remove _skip_if_hg_missing() from vcs_hgconfig and set_vcs_hgconfig

why: add_doctest_fixtures declared the per-VCS repo factories
(create_git_remote_repo, create_svn_remote_repo, create_hg_remote_repo,
git_repo) as parameters, so pytest instantiated all of them before the
body's `if shutil.which(...)` guards ran. Each factory pulls in a
binary-invoking fixture, so a single missing binary (e.g. hg) skipped
the whole fixture and therefore every doctest -- including doctests for
the binaries that were present.

what:
- Drop the per-VCS fixtures from the signature; request them via
  request.getfixturevalue() inside each `if shutil.which(...)` block
- A missing binary now drops only that VCS's doctest helpers; doctests
  for the present binaries still run

why: The svn fixtures build repositories with `svnadmin`, and
_skip_if_svn_missing() treats svn as available only when both the svn
client and svnadmin are present. The public skip_if_svn_missing mark and
the pytest_ignore_collect hook checked the svn client alone, so on a
host with svn but not svnadmin they disagreed with the fixtures: a
mark-decorated test would run, and svn doctest modules would be
collected while their create_svn_remote_repo namespace helper -- which
also requires svnadmin -- was withheld, erroring with NameError instead
of skipping. Make every svn-availability check require svnadmin.

what:
- Add the svnadmin check to the skip_if_svn_missing mark condition
- Require svnadmin in pytest_ignore_collect so svn modules are ignored
  (not collected) when only the svn client is present

why: git 2.54 changed `git remote set-head` output: when origin/HEAD
already points at the branch it prints "'origin/HEAD' is unchanged and
points to 'master'" instead of "origin/HEAD set to master". The doctest
asserted the older literal string, so it failed under the git on CI.
The failure is independent of the pytest 9.1 fixture changes -- it was
latent until the plugin could import and the suite actually ran.

what:
- Assert version-stable invariants instead of the literal message:
  `'master' in set_head(auto=True)` and that `set_head('master')`
  returns a str