pre-release tests with avocado-static-checks submodule

The pre-release checks don't checkout avocado-static-checks submodule,
which is mandatory for running static-check after 8639fdb. This is a fix
for that.

Referencei: 8639fdb
Signed-off-by: Jan Richter <jarichte@redhat.com>

.github/workflows/prerelease.yml

@@ -15,6 +15,7 @@ jobs:
       - uses: actions/checkout@v4
         with:
           fetch-depth: 0
+          submodules: true
       - name: Set up Python 3.9
         uses: actions/setup-python@v5
         with: