fix(realization-view): Add styling for all individual layers

Co-authored-by: Ernst Würger <ewuerger@users.noreply.github.com>

capellambse_context_diagrams/__init__.py

@@ -184,6 +184,6 @@ def register_realization_view() -> None:
             "realization_view",
             context.RealizationViewContextAccessor("Realization Diagram"),
         )
-        styles |= capstyle.STYLES.get(dgcls.value, {})
+        styles.update(capstyle.STYLES.get(dgcls.value, {}))
 
     capstyle.STYLES["Realization Diagram"] = styles