Flow FullAssemblySigningSupported for source-build to repo tasks (#47421

)

This property is being added to arcade via
dotnet/arcade#12749 and
dotnet/arcade#12940

Once this property is added to arcade, it flows correctly to the main
aspnetcore build, but not to the build for repo tasks. The repo tasks
still need this, otherwise they end up using full signing.

Fix that by manually passing the property along (using env var) when
building the repo tasks.

eng/SourceBuild.props

@@ -40,6 +40,11 @@
       <_AdditionalRepoTaskBuildArgs Condition="'$(DotNetRuntimeSourceFeedKey)' != ''" >$(_AdditionalRepoTaskBuildArgs) --runtimesourcefeedkey $(DotNetRuntimeSourceFeedKey)</_AdditionalRepoTaskBuildArgs>
     </PropertyGroup>
 
+    <ItemGroup>
+      <!-- We need to flow FullAssemblySigningSupported even when building repo tasks because they use full signing -->
+      <InnerBuildEnv Condition="'$(FullAssemblySigningSupported)' != ''" Include="FullAssemblySigningSupported=$(FullAssemblySigningSupported)" />
+    </ItemGroup>
+
     <!-- Call the build.sh script to build the repo tasks. Set IgnoreStandardErrorWarningFormat
          to true. This avoids fatal errors, because in internal builds there are usually a few failed installation
          attempts as the install script walks through potential locations for a runtime.