Disable F# test project signing unconditionally

The F# compiler produces assemblies with malformed public key blobs
when public-signing with full key pairs on Unix (dotnet/fsharp#19441).
Previously SignAssembly was only disabled for source-build, but the
fix for dotnet/fsharp#19242 exposed this on all Unix legs.

Since this is a non-shipping test project, disable signing
unconditionally as a workaround.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: steveisok

src/libraries/System.Formats.Cbor/tests/CborDocument/System.Formats.Cbor.Tests.DataModel.fsproj

@@ -4,8 +4,8 @@
     <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
     <!-- NuGet restore issue with TargetFrameworks in f# projects: https://github.com/NuGet/Home/issues/10005 -->
     <TargetFramework>$(NetCoreAppCurrent)</TargetFramework>
-    <!-- Public signing (performed under DotNetBuildSourceOnly) is broken for f#: https://github.com/dotnet/fsharp/issues/17451 -->
-    <SignAssembly Condition="'$(DotNetBuildSourceOnly)' == 'true'">false</SignAssembly>
+    <!-- F# public signing with full key pairs produces malformed public key blobs on Unix: https://github.com/dotnet/fsharp/issues/19441 -->
+    <SignAssembly>false</SignAssembly>
   </PropertyGroup>
 
   <ItemGroup>