udpate release notes with path release

Author: FabianHofmann

doc/release_notes.rst

@@ -25,6 +25,11 @@ Upcoming Version
 * Fix Xpress IIS label mapping for masked constraints and add a regression test for matching infeasible coordinates.
 * Enable quadratic problems with SCIP on windows.
 * Add ``fix()``, ``unfix()``, and ``fixed`` to ``Variable`` and ``Variables`` for fixing variables to values via equality constraints. Supports automatic rounding and optional integrality relaxation (``relax=True``) for MILP dual extraction.
+
+
+Version 0.6.6
+-------------
+
 * Free the knitro context and compute necessary quantities within linopy. Knitro context is not exposed anymore.