Ensure HW intrinsics enabled when running arm64 longmul tests. (dotne…

…t#92607)

Currently, when jitstress runs the HWIntrinsics disabled environment
for JIT opts, this test will fall over as it must have hardware
intrinsics enabled to detect the correct assembly output.

This patch simply forces on DOTNET_EnableHWIntrinsic to ensure the
test will always function correctly.

src/tests/JIT/opt/Multiply/MultiplyLongOps.csproj

@@ -14,5 +14,6 @@
 
     <CLRTestEnvironmentVariable Include="DOTNET_TieredCompilation" Value="0" />
     <CLRTestEnvironmentVariable Include="DOTNET_JITMinOpts" Value="0" />
+    <CLRTestEnvironmentVariable Include="DOTNET_EnableHWIntrinsic" Value="1" />
   </ItemGroup>
 </Project>