Dashboard: Scene Migration: Add variable definition prop to serialization (#79022)

Co-authored-by: Ivan Ortega Alba <ivanortegaalba@gmail.com>

package.json

@@ -256,7 +256,7 @@
     "@grafana/lezer-traceql": "0.0.11",
     "@grafana/monaco-logql": "^0.0.7",
     "@grafana/runtime": "workspace:*",
-    "@grafana/scenes": "^1.24.6",
+    "@grafana/scenes": "^1.26.0",
     "@grafana/schema": "workspace:*",
     "@grafana/ui": "workspace:*",
     "@kusto/monaco-kusto": "^7.4.0",