Update FSharp.Test.Utilities.fsproj (#15197)

Fixes 
```
Testhost process for source(s) 'C:\Users\vlza\code\fsharp3\artifacts\bin\FSharp.Test.Utilities\Debug\net7.0\FSharp.Test.Utilities.dll' exited with error: Error:
  An assembly specified in the application dependencies manifest (FSharp.Test.Utilities.deps.json) was not found:
    package: 'FluentAssertions', version: '5.10.3'
    path: 'lib/netcoreapp2.1/FluentAssertions.dll'
. Please check the diagnostic logs for more information.
```
When running with `dotnet test` on whole solution.

Co-authored-by: Kevin Ransom (msft) <[email protected]>

Author: vzarytovskii

tests/FSharp.Test.Utilities/FSharp.Test.Utilities.fsproj

@@ -11,6 +11,7 @@
     <Optimize>false</Optimize>
     <Tailcalls>false</Tailcalls>
     <OtherFlags>$(OtherFlags) --warnon:1182</OtherFlags>
+    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
   </PropertyGroup>
 
   <ItemGroup>