test(common): Simplify next_version tests - use fixed version string

why: The _get_next_tmux_version() helper duplicates version parsing logic
already in common.py and is unnecessary for testing prefix stripping.
what:
- Remove _get_next_tmux_version() helper from both test files
- Use fixed "3.9" version string instead of calculated version
- Remove unrelated has_gt_version(TMUX_MAX_VERSION) assertion
- Test focuses on parsing "next-X.Y" strings, not version comparison

Author: tony

tests/legacy_api/test_common.py

@@ -53,11 +53,10 @@ def mock_tmux_cmd(*args: t.Any, **kwargs: t.Any) -> Hi:
 
 
 def test_allows_next_version(monkeypatch: pytest.MonkeyPatch) -> None:
-    """Assert get_version() supports next version."""
-    TMUX_NEXT_VERSION = "3.6"
+    """Assert get_version() supports next-prefixed versions."""
 
     class Hi:
-        stdout: t.ClassVar = [f"tmux next-{TMUX_NEXT_VERSION}"]
+        stdout: t.ClassVar = ["tmux next-3.9"]
         stderr = None
 
     def mock_tmux_cmd(*args: t.Any, **kwargs: t.Any) -> Hi:
@@ -67,8 +66,7 @@ def mock_tmux_cmd(*args: t.Any, **kwargs: t.Any) -> Hi:
 
     assert has_minimum_version()
     assert has_gte_version(TMUX_MIN_VERSION)
-    assert has_gt_version(TMUX_MAX_VERSION), "Greater than the max-supported version"
-    assert get_version() == TMUX_NEXT_VERSION
+    assert get_version() == "3.9"
 
 
 def test_get_version_openbsd(monkeypatch: pytest.MonkeyPatch) -> None:

tests/test_common.py

@@ -298,10 +298,10 @@ class VersionParsingFixture(t.NamedTuple):
     ),
     VersionParsingFixture(
         test_id="next_version",
-        mock_stdout=["tmux next-3.6"],
+        mock_stdout=["tmux next-3.9"],
         mock_stderr=None,
         mock_platform=None,
-        expected_version="3.6",
+        expected_version="3.9",
         raises=False,
         exc_msg_regex=None,
     ),
@@ -363,7 +363,6 @@ def mock_tmux_cmd(*args: t.Any, **kwargs: t.Any) -> MockTmuxOutput:
         assert get_version() == expected_version
         assert has_minimum_version()
         assert has_gte_version(TMUX_MIN_VERSION)
-        assert has_gt_version(TMUX_MAX_VERSION)
 
 
 class VersionValidationFixture(t.NamedTuple):