github: + catch2 install (for xo-indentlog)

.github/workflows/main-stock-ubuntu.yml

@@ -21,6 +21,11 @@ jobs:
       - name: checkout source
         uses: actions/checkout@v3
 
+      - name: Install catch2
+        # install catch2.
+        # see [[https://stackoverflow.com/questions/57982945/how-to-apt-get-install-in-a-github-actions-workflow]]
+        run: sudo apt-get install -y catch2
+
       - name: bootstrap xo-cmake
         run: |
           PREFIX=${{github.workspace}}/local