ci: run make sparse as part of the GitHub workflow

Occasionally we receive reviews after patches were integrated, where
`sparse` (https://sparse.docs.kernel.org/en/latest/ has more information
on that project) identified problems such as file-local variables or
functions being declared as global.

By running `sparse` as part of our Continuous Integration, we can catch
such things much earlier. Even better: developers who activated GitHub
Actions on their forks can catch such issues before even sending their
patches to the Git mailing list.

This addresses gitgitgadget#345

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/workflows/main.yml

@@ -350,6 +350,14 @@ jobs:
     - uses: actions/checkout@v1
     - run: ci/install-dependencies.sh
     - run: ci/run-static-analysis.sh
+  sparse:
+    runs-on: ubuntu-20.04
+    steps:
+    - name: Install `sparse` and other dependencies
+      run: |
+        sudo apt-get install -q -y sparse libssl-dev libcurl4-openssl-dev libexpat-dev gettext zlib1g-dev
+    - uses: actions/checkout@v2
+    - run: make sparse
   documentation:
     needs: ci-config
     if: needs.ci-config.outputs.enabled == 'yes'