httpclient: clear client->parser.data after use

ntlmclient: update to latest upstream ntlmclient

git_diff_find_similar doesn't always remove unmodified deltas

Some static code analysis complains that we're putting a stack variable
into client->parser.data (which persists past the function calls). Clear
that on function exit to avoid confusion.

Fix some bugs caught by UBscan

`git_commit_create_v` takes _commits_ not _commit ids_. Fix the test to
call the API correctly.

Passing a function pointer with different parameters is UB, even if
those params are (void *). Use our separate `_cb` functions that will do
the correct casting.

zlib: upgrade bundled zlib to v1.3

examples: use unsigned int for bitfields

Bypass shallow clone support for in-memory repositories

blame example: Fix support for line range in CLI

Minor bug fixes

ci: improvements to prepare for Cygwin support

Ensure that the main builds are all identical in nightly. Nightly should
only add new, specialized builds.

Setup scripts can change BUILD_WORKSPACE, for instance, if they use a
different format for paths, they can replace with `cygpath` variants.

Allow the build matrix to specify its shell, in case we provide one in
the setup (eg, Cygwin).

Always checkout out shell scripts with Unix-style line endings. mingw
doesn't mind, but cygwin struggles without CRLF.

`opts` may be null; check before dereferencing.

`GIT_ASSERT` may be a macro for `assert` (when `GIT_ASSERT_HARD` is
defined), which may differ in debug builds. Pull the assignment out of
the assertion.

If we're reading an on-disk packfile, ensure that we close the file
descriptor on error.

CI fixes

tests: remove test for strcasecmp

process: don't try to close the status

Previously, users could skip certain tests when running the CI script
(`SKIP_ONLINE_TESTS=1`). Provide a mechanism for users to opt-in to
only certain tests (`SKIP_TESTS=1 SKIP_ONLINE_TESTS=0`).

README: replace gmaster with GitButler

`process->status` is a status value; we were mistakenly trying to close
it as a file descriptor, as if it were the `status` self-pipe that we open
during process creation.

Instead, don't try to close it, as it's not a file descriptor.

master is no more; GitButler is a new client using libgit2.

Fixes #6689

It was unused and only defined in posix.h
It did not exist in its Windows equivalent.

strcasecmp is a posix function, testing it doesn't make sense.
Functions that needs unsigned compare should use git__strcasecmp()

cli: add `index-pack` command

ci: allow workflows to push changes

Our workflows push documentation changes; ensure that they are allowed
to do so.