github: Get sparse from the official GitHub mirror.

We had a few issues lately with GitHub Actions being unable to checkout
sparse from the git.kernel.org:

  git clone git://git.kernel.org/pub/scm/devel/sparse/sparse.git
  Cloning into 'sparse'...
  fatal: unable to connect to git.kernel.org:
  git.kernel.org[0: 172.105.4.254]: errno=Connection timed out
  git.kernel.org[1: 2600:3c04::f03c:95ff:fe5e:7468]: errno=Network is unreachable

Let's try and use the official mirror of the project hosted on GitHub
itself.  This mirror is maintained by the main maintainer of the
project and mentioned in the documentation as one of the ways of
getting sparse:
  https://sparse.docs.kernel.org/en/latest/#getting-sparse

It may also be better to not create extra load on kernel.org servers,
they should not be used for CI purposes.

Note: we only need to get sparse for one type of jobs.  All other jobs
that call linux-prepare.sh do not actually use sparse (clang jobs and
the debian job are not using sparse).

Acked-by: Mike Pattrick <mkp@redhat.com>
Acked-by: Kevin Traynor <ktraynor@redhat.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Signed-off-by: Ilya Maximets <i.maximets@ovn.org>

.ci/linux-prepare.sh

@@ -12,10 +12,11 @@ fi
 #
 # Disabling sqlite support because sindex build fails and we don't
 # really need this utility being installed.
-git clone git://git.kernel.org/pub/scm/devel/sparse/sparse.git
-cd sparse
-make -j4 HAVE_SQLITE= install
-cd ..
+if test -d sparse; then
+    pushd sparse
+    make -j4 HAVE_SQLITE= install
+    popd
+fi
 
 # Installing wheel separately because it may be needed to build some
 # of the packages during dependency backtracking and pip >= 22.0 will

.github/workflows/build-and-test.yml

@@ -306,6 +306,13 @@ jobs:
       if:   matrix.m32 != ''
       run:  sudo apt install -y gcc-multilib
 
+    - name: checkout sparse
+      uses: actions/checkout@v4
+      # Official mirror of the git.kernel.org/pub/scm/devel/sparse/sparse.git.
+      with:
+        repository: lucvoo/sparse
+        path: sparse
+
     - name: prepare
       run:  ./.ci/linux-prepare.sh