Update release notes

Author: LauWien

RELEASE_NOTES.rst

@@ -4,6 +4,7 @@ Next release
 All changes
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+- Adjust test suite for pyam v1.1.0 compatibility (:pull:`499`).
 - Update reference for activity and capacity soft constraints (:pull:`474`).
 - Update :meth:`.years_active` to use sorted results (:pull:`491`).
 - Adjust the Westeros reporting tutorial to pyam 1.0 deprecations (:pull:`492`).