ci: lint only with latest RF

Author: aaltat

.github/workflows/on-push.yml

@@ -35,6 +35,7 @@ jobs:
       run: |
         uv pip install robotframework==${{ matrix.rf-version }} --python ${{ matrix.python-version }} --system
     - name: Lint files
+      if : matrix.rf-version != '6.1.1'
       run: |
         inv lint -e
     - name: Run unit tests