ruff: simplify version retrieval logic in __init__.py

Author: edwardchalstrey1

src/pygambit/__init__.py

@@ -36,7 +36,4 @@
     # Package is not installed, fallback to reading GAMBIT_VERSION file
     import pathlib
     _version_file = pathlib.Path(__file__).parent.parent.parent / "GAMBIT_VERSION"
-    if _version_file.exists():
-        __version__ = _version_file.read_text().strip()
-    else:
-        __version__ = "unknown"
+    __version__ = _version_file.read_text().strip() if _version_file.exists() else "unknown"