ci: Move to actions/checkout@v3 version

v2 has been deprecated for a long time, and is throwing warnings.

.github/workflows/build.yml

@@ -7,7 +7,7 @@ jobs:
       image: fedora:rawhide
       options: --security-opt seccomp=unconfined
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - run: dnf install --nogpgcheck -y git-core checkpolicy policycoreutils-devel make m4 findutils
       - run: git clone --depth=1 https://github.com/containers/container-selinux.git /tmp/container-selinux
       - run: cp /tmp/container-selinux/container.* policy/modules/contrib
@@ -21,7 +21,7 @@ jobs:
       options: --security-opt seccomp=unconfined
     steps:
       - run: dnf install --nogpgcheck -y make git-core rpm-build 'dnf-command(builddep)'
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       # https://github.blog/2022-04-12-git-security-vulnerability-announced/
       - run: git config --global --add safe.directory /__w/selinux-policy/selinux-policy
       - run: make -C .copr srpm outdir="$PWD"