Update release_notes.rst

Author: tgilon

docs/release_notes.rst

@@ -23,6 +23,7 @@ Upcoming Release
 * Include unit test execution and compile_cost_assumptions_usa.py in ci.yaml (https://github.com/PyPSA/technology-data/pull/174)
 
 * Align `snakemake` version and the related `mock_snakemake` to PyPSA-Eur (https://github.com/PyPSA/technology-data/pull/177)
+
 * Improve filename consistency in the sources (https://github.com/PyPSA/technology-data/pull/178)
 
 * Include further unit tests for compile_cost_assumptions_usa.py (https://github.com/PyPSA/technology-data/pull/182)