tests: repin PyQt6 packages to v6.6.0

Fix test failures caused by mismatch between the pinned PyQt6
package and unpinned corresponding PyQt6-Qt6 package.

tests/requirements-libraries.txt

@@ -41,13 +41,13 @@ PyQtPurchasing==5.15.5
 QScintilla==2.14.1
 PyQtWebEngine==5.15.6
 # PyQt6 and add-on packages
-PyQt6==6.5.3
-PyQt6-3D==6.5.0
-PyQt6-Charts==6.5.0
-PyQt6-DataVisualization==6.5.0
-PyQt6-NetworkAuth==6.5.0
+PyQt6==6.6.0
+PyQt6-3D==6.6.0
+PyQt6-Charts==6.6.0
+PyQt6-DataVisualization==6.6.0
+PyQt6-NetworkAuth==6.6.0
 PyQt6-QScintilla==2.14.1
-PyQt6-WebEngine==6.5.0
+PyQt6-WebEngine==6.6.0
 python-dateutil==2.8.2
 pytz==2023.3.post1
 requests==2.31.0