Don't add newlines to the start of docstrings

[AlexWaygood]

This edit means that the docstrings inserted by the codemod look closer to what they look like upstream in the CPython source code. We should see a diff like this following the next typeshed sync, after we update the pinned commit of docstring-adder in Ruff to one that includes this PR:

diff --git a/stdlib/__future__.pyi b/stdlib/__future__.pyi
index 76ecfca2c..ce4442d92 100644
--- a/stdlib/__future__.pyi
+++ b/stdlib/__future__.pyi
@@ -55,15 +55,13 @@ _VersionInfo: TypeAlias = tuple[int, int, int, str, int]
 class _Feature:
     def __init__(self, optionalRelease: _VersionInfo, mandatoryRelease: _VersionInfo | None, compiler_flag: int) -> None: ...
     def getOptionalRelease(self) -> _VersionInfo:
-        """
-        Return first release in which this feature was recognized.
+        """Return first release in which this feature was recognized.
 
         This is a 5-tuple, of the same form as sys.version_info.
         """
 
     def getMandatoryRelease(self) -> _VersionInfo | None:
-        """
-        Return release in which this feature will become mandatory.
+        """Return release in which this feature will become mandatory.
 
         This is a 5-tuple, of the same form as sys.version_info, or, if
         the feature was dropped, or the release date is undetermined, is None.
diff --git a/stdlib/_asyncio.pyi b/stdlib/_asyncio.pyi
index 3a3721dad..ef0f8e0d7 100644
--- a/stdlib/_asyncio.pyi
+++ b/stdlib/_asyncio.pyi
@@ -15,8 +15,7 @@ _T_co = TypeVar("_T_co", covariant=True)
 _TaskYieldType: TypeAlias = Future[object] | None
 
 class Future(Awaitable[_T]):
-    """
-    This class is *almost* compatible with concurrent.futures.Future.
+    """This class is *almost* compatible with concurrent.futures.Future.
 
     Differences:
 
@@ -41,20 +40,15 @@ class Future(Awaitable[_T]):
     _asyncio_future_blocking: bool  # is a part of duck-typing contract for `Future`
     def __init__(self, *, loop: AbstractEventLoop | None = ...) -> None: ...
     def __del__(self) -> None:
-        """
-        Called when the instance is about to be destroyed.
-        """
+        """Called when the instance is about to be destroyed."""
 
     def get_loop(self) -> AbstractEventLoop:
-        """
-        Return the event loop the Future is bound to.
-        """
+        """Return the event loop the Future is bound to."""
 
     @property
     def _callbacks(self) -> list[tuple[Callable[[Self], Any], Context]]: ...
     def add_done_callback(self, fn: Callable[[Self], object], /, *, context: Context | None = None) -> None:
-        """
-        Add a callback to be run when the future becomes done.
+        """Add a callback to be run when the future becomes done.
 
         The callback is called with a single argument - the future object. If
         the future is already done when this is called, the callback is
@@ -62,8 +56,7 @@ class Future(Awaitable[_T]):
         """
 
     def cancel(self, msg: Any | None = None) -> bool:
-        """
-        Cancel the future and schedule callbacks.
+        """Cancel the future and schedule callbacks.
 
         If the future is already done or cancelled, return False.  Otherwise,
         change the future's state to cancelled, schedule the callbacks and