Bump System.Linq.Dynamic.Core from 1.6.7 to 1.6.8

---
updated-dependencies:
- dependency-name: System.Linq.Dynamic.Core
  dependency-version: 1.6.8
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

samples/snippets/visualbasic/programming-guide/dynamic-linq-expression-trees/dynamic-linq-expression-trees.vbproj

@@ -9,7 +9,7 @@
   <ItemGroup>
     <PackageReference Include="ExpressionTreeToString" Version="3.4.71" />
     <PackageReference Include="LinqKit.Core" Version="1.2.8" />
-    <PackageReference Include="System.Linq.Dynamic.Core" Version="1.6.7" />
+    <PackageReference Include="System.Linq.Dynamic.Core" Version="1.6.8" />
   </ItemGroup>
 
   <ItemGroup>