fix(tests): skip format expansion test on tmux <3.2

Format expansion in style options (e.g., fg=#{...}) was added in
tmux 3.2 (commit f03b6113). Earlier versions reject styles with
format syntax as invalid.

Verification from tmux source code:
- Examined cmd-set-option.c in tmux 3.2 (commit f03b6113)
- Found validation logic: styles WITH #{...} skip validation
- Styles WITHOUT #{...} are still validated
- In tmux <3.2, ALL styles are validated, rejecting #{...} syntax

From commit f03b6113 message:
"Any styles without a '#{' are still validated when they are set
but any with a '#{' are not."

From cmd-set-option.c after f03b6113:
```c
if ((oe->flags & OPTIONS_TABLE_IS_STYLE) &&
    strstr(value, "#{") == NULL &&
    style_parse(&sy, &grid_default_cell, value) != 0) {
```

The test now only runs the format expansion check on tmux 3.2+.

References:
- tmux commit f03b6113 (style format expansion support)
- cmd-set-option.c validation logic with strstr check

Author: tony

tests/test_options.py

@@ -612,11 +612,12 @@ def test_style_option_validation(server: Server) -> None:
             # tmux <3.2: bold→bright
             assert style == "fg=colour240,bg=#525252,bright,underscore"
 
-        # Test style with variables
-        session.set_option("status-style", "fg=#{?pane_in_mode,red,green}")
-        style = session.show_option("status-style")
-        assert isinstance(style, str)
-        assert style == "fg=#{?pane_in_mode,red,green}"
+        # Test style with variables (format expansion added in tmux 3.2)
+        if has_gte_version("3.2"):
+            session.set_option("status-style", "fg=#{?pane_in_mode,red,green}")
+            style = session.show_option("status-style")
+            assert isinstance(style, str)
+            assert style == "fg=#{?pane_in_mode,red,green}"
 
 
 def test_option_error_handling(server: Server) -> None: