Now I have the relevant code. The issue is clear:

1. In `groupby.py` line 439, the `__repr__` method has a trailing space before `\n`:
   ```python
   return "{}, grouped over {!r} \n{!r} groups with labels {}.".format(
   ```
   The space after `{!r}` and before `\n` is causing the trailing whitespace.

2. The tests in `test_groupby.py` also have the trailing space to match the current (incorrect) output:
   - Line 394: `expected += ", grouped over %r " % dim`
   - Line 408: `expected += ", grouped over 'month' "`

Let me generate the patch to fix this:

--- a/xarray/core/groupby.py
+++ b/xarray/core/groupby.py
@@ -436,7 +436,7 @@ class GroupBy(SupportsArithmetic):
         return zip(self._unique_coord.values, self._iter_grouped())
 
     def __repr__(self):
-        return "{}, grouped over {!r} \n{!r} groups with labels {}.".format(
+        return "{}, grouped over {!r}\n{!r} groups with labels {}.".format(
             self.__class__.__name__,
             self._unique_coord.name,
             self._unique_coord.size,
--- a/xarray/tests/test_groupby.py
+++ b/xarray/tests/test_groupby.py
@@ -391,7 +391,7 @@ def test_groupby_repr(obj, dim):
     actual = repr(obj.groupby(dim))
     expected = "%sGroupBy" % obj.__class__.__name__
-    expected += ", grouped over %r " % dim
+    expected += ", grouped over %r" % dim
     expected += "\n%r groups with labels " % (len(np.unique(obj[dim])))
     if dim == "x":
         expected += "1, 2, 3, 4, 5."
@@ -405,7 +405,7 @@ def test_groupby_repr(obj, dim):
 @pytest.mark.parametrize("obj", [repr_da, repr_da.to_dataset(name="a")])
 def test_groupby_repr_datetime(obj):
     actual = repr(obj.groupby("t.month"))
     expected = "%sGroupBy" % obj.__class__.__name__
-    expected += ", grouped over 'month' "
+    expected += ", grouped over 'month'"
     expected += "\n%r groups with labels " % (len(np.unique(obj.t.dt.month)))
     expected += "1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12."
     assert actual == expected