Update version tag to 14.12.0-rc.1 in Directory.Build.props

Transitioned the version tag in the `Directory.Build.props` file from
`14.12.0-beta.1` to `14.12.0-rc.1`, indicating a move from beta to
release candidate. This change reflects increased stability and
feature completeness as we approach the final release.

src/Directory.Build.props

@@ -5,6 +5,6 @@
     <Copyright>(C) 2024 [email protected]</Copyright>
     <AssemblyVersion>14.12.0.0</AssemblyVersion>
     <FileVersion>14.12.0.0</FileVersion>
-    <Version>14.12.0-beta.1</Version>
+    <Version>14.12.0-rc.1</Version>
   </PropertyGroup>
 </Project>