CI: Continue on error if tmux@master

Author: tony

.github/workflows/libtmux-ci.yml

@@ -49,6 +49,7 @@ jobs:
       run: |
         pipenv run flake8
     - name: Test with pytest
+      continue-on-error: ${{ matrix.tmux-version == 'master' }}
       run: |
         export PATH=$HOME/tmux-builds/tmux-${{ matrix.tmux-version }}/bin:$PATH
         ls $HOME/tmux-builds/tmux-${{ matrix.tmux-version }}/bin