build(deps): libtmux 0.20.0 -> 0.21.0 to avoid isolated crashes

This adjusts the default separator for formats to be a pipe (somewhat
common in the terminal) to a rare character - ␞. This will avoid crashes
with various libtmux lookups.

See also:
- tmux-python/libtmux#475
- https://github.com/tmux-python/libtmux/releases/tag/v0.21.0

Author: tony

poetry.lock

@@ -47,7 +47,7 @@ tmuxp = 'tmuxp:cli.cli'
 
 [tool.poetry.dependencies]
 python = "^3.7"
-libtmux = "~0.20.0"
+libtmux = "~0.21.0"
 colorama = ">=0.3.9"
 PyYAML = "^6.0"