f2/testlib/fixtures/env: home cannot be None

Is there a situation where `home` can be None? This hinders the ability
to use it quickly without type gating in the test code itself.

Change-Id: Idd739ddad67e10d6f7a6aad283c0e3b7cd08106a
Signed-off-by: Raito Bezarius <raito@lix.systems>

tests/functional2/testlib/fixtures/env.py

@@ -137,7 +137,7 @@ class _ManagedPath:
 @dataclasses.dataclass
 class _Dirs:
     test_root: Path | None
-    home: Path | None
+    home: Path
     nix_log_dir: Path | None
     nix_state_dir: Path | None
     nix_conf_dir: Path | None