fix merged release notes

doc/release_notes.rst

@@ -4,15 +4,6 @@ Release Notes
 Upcoming Version
 ----------------
 
-**Bug fixes**
-
-* A multi-key ``groupby`` now returns its groups sorted by key tuple, like the single-key path. The key combinations were numbered by iterating a ``set``, so the group order was arbitrary and changed between processes with ``PYTHONHASHSEED``.
-
-
-Version 0.9.1
--------------
-
-**Features**
 
 *Strict "v1" arithmetic semantics (opt-in)*
 
@@ -59,6 +50,17 @@ Version 0.9.1
 * Mutation via assignment to ``Variable.lower`` / ``Variable.upper`` / ``Constraint.coeffs`` / ``Constraint.vars`` / ``Constraint.lhs`` / ``Constraint.sign`` / ``Constraint.rhs`` is deprecated and emits a ``DeprecationWarning``. Use ``Variable.update(...)`` / ``Constraint.update(...)`` instead — the canonical mutation API with one validation path and one place that flips the persistent-solver dirty flag. Read access to these properties is unchanged. The setters will be removed in a future release.
 * Passing a raw ``DataArray`` of integer labels to ``Constraint.vars = ...`` setter is deprecated and emits a ``FutureWarning``. Pass a ``Variable`` to ``Constraint.update()`` instead — it is the supported input. The ``DataArray`` path will be removed in a future release.
 
+
+**Bug fixes**
+
+* A multi-key ``groupby`` now returns its groups sorted by key tuple, like the single-key path. The key combinations were numbered by iterating a ``set``, so the group order was arbitrary and changed between processes with ``PYTHONHASHSEED``.
+
+
+Version 0.9.1
+-------------
+
+**Features**
+
 *Named expressions*
 
 * You can now store expressions in the model and get them back by name. ``Model.add_expressions`` registers a ``LinearExpression`` or ``QuadraticExpression`` under a name (auto-named ``expr0``, ``expr1``, ... if you don't pass one). Registered expressions live in ``Model.expressions``, a container that works like ``Model.variables`` and ``Model.constraints``, and are removed with ``Model.remove_expressions``. They survive ``Model.to_netcdf``/``linopy.read_netcdf``, ``Model.copy``, ``copy.copy``, ``copy.deepcopy`` and pickling. (`#882 <https://github.com/PyPSA/linopy/pull/882>`__)