fix: resolve ruff v0.15.0 linter errors

- PYI034: Use `Self` return type for `__enter__` in SCMContext
- PLW0108: Replace unnecessary lambda with direct `bool` reference

https://claude.ai/code/session_01M18n2k6KLenwMRANgSFMXc

dvc/repo/scm_context.py

@@ -10,6 +10,8 @@ from dvc.utils import relpath
 from dvc.utils.collections import ensure_list
 
 if TYPE_CHECKING:
+    from typing_extensions import Self
+
     from dvc.repo import Repo
     from dvc.scm import Base
 
@@ -131,7 +133,7 @@ class SCMContext:
 
         self.files_to_track = set()
 
-    def __enter__(self) -> "SCMContext":
+    def __enter__(self) -> "Self":
         self._cm = self()
         return self._cm.__enter__()
 

tests/unit/command/test_help.py

@@ -47,7 +47,7 @@ def test_help(caplog, capsys, command_tuples):
     out, err = capsys.readouterr()
 
     # validate metavars are all in lowercase
-    usage = "\n".join(takewhile(lambda o: bool(o), out.splitlines()))
+    usage = "\n".join(takewhile(bool, out.splitlines()))
 
     message = (
         "metavars not lowercased, you are likely missing formatter_class=XXX "