ci: Run shellcheck in CI linter job

Install and run shellcheck in the CI linter job. Lint all files matching
'*.sh' in the tree.

Signed-off-by: Felix Matouschek <fmatouschek@redhat.com>

.github/workflows/ci.yml

@@ -34,10 +34,11 @@ jobs:
           python-version: 3.x
           cache: pip
 
-      - name: Install yamllint, ansible
+      - name: Install yamllint, ansible, shellcheck
         run: |
           python -m pip install --upgrade pip
           pip install yamllint ansible-core ansible-lint
+          sudo apt install -y shellcheck
 
       - name: Run yamllint
         run: |
@@ -50,6 +51,11 @@ jobs:
           ansible-lint -v
         working-directory: ${{ env.collection_dir }}
 
+      - name: Run shellcheck
+        run: |
+          find . -type f -iname '*.sh' -exec shellcheck {} \;
+        working-directory: ${{ env.collection_dir }}
+
   sanity:
     uses: ansible-network/github_actions/.github/workflows/sanity.yml@main
     needs: