chore: bump version to 4.13.0 for release

RELEASE_NOTES.md already captures all changes included in 4.13.0:
- Fable 5 upgrade + .NET SDK 10.0 CI fixes
- AsyncSeq.ofList, AsyncSeq.ofArray, AsyncSeq.cycle
- Fix deprecated F# refcell operators (! and :=)

Co-authored-by: Copilot <[email protected]>

Author: github-actions[bot]

version.props

@@ -1,5 +1,5 @@
 <Project>
   <PropertyGroup>
-    <Version>4.12.0</Version>
+    <Version>4.13.0</Version>
   </PropertyGroup>
 </Project>