Bump Eto.Platform.Gtk from 2.11.0 to 2.12.0 (#74)

---
updated-dependencies:
- dependency-name: Eto.Platform.Gtk
  dependency-version: 2.12.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

GlennGUI/GlennGUI.Gtk/GlennGUI.Gtk.csproj

@@ -11,7 +11,7 @@
     </ItemGroup>
 
     <ItemGroup>
-        <PackageReference Include="Eto.Platform.Gtk" Version="2.11.0" />
+        <PackageReference Include="Eto.Platform.Gtk" Version="2.12.0" />
     </ItemGroup>
 
 </Project>