pr-ci: Check out submodules, needed if any of them changed

When CI is run per commit, we first checkout the base branch and then we
merge in the "commit under review". Checking out the submodules from the
base is not going to be the correct ones. We need to check out the
submodules from the "commit under review".

.github/workflows/pr-ci.yml

@@ -57,7 +57,6 @@ jobs:
       - name: Clone the repo
         uses: actions/checkout@v4
         with:
-          submodules: recursive
           fetch-depth: 0
           ref: ${{ github.event.pull_request.base.sha }}
 
@@ -70,6 +69,7 @@ jobs:
         run: |
           git fetch origin ${{ matrix.commit }} ${{ github.event.pull_request.merge_commit_sha }}
           git merge --no-ff --no-edit ${{ matrix.commit }}
+          git submodule update --init --recursive
           git log -1 --format="Head %H, Parents %P"
           # Since the workflow definition is taken from the pull request merge commit, we need to
           # get the .ci scripts from there as well.