ci(tests): Add tests for tmux 3.3a

See also: https://raw.githubusercontent.com/tmux/tmux/3.3a/CHANGES

Author: tony

.github/workflows/tests.yml

@@ -11,7 +11,7 @@ jobs:
     strategy:
       matrix:
         python-version: ["3.7", "3.10"]
-        tmux-version: ["2.6", "2.7", "2.8", "3.0a", "3.1b", "3.2a", "master"]
+        tmux-version: ["2.6", "2.7", "2.8", "3.0a", "3.1b", "3.2a", "3.3a", "master"]
     steps:
       - uses: actions/checkout@v3