Add CITATION.cff validation to lint workflow

Author: yarikoptic

.github/workflows/lint.yml

@@ -22,6 +22,10 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           python -m pip install --upgrade tox
+          python -m pip install --upgrade cffconvert pyyaml
 
       - name: Run linters
         run: tox -e lint
+
+      - name: Validate CITATION.cff
+        run: cffconvert --validate