Fix _PrepareNativeAssemblySources Outputs typo (typemaps → typemap)

The target declared Outputs as typemaps.{abi}.ll but GenerateEmptyTypemapStub
writes typemap.{abi}.ll. The mismatch caused MSBuild to always rerun the target.

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

Author: simonrozsival

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.Trimmable.targets

@@ -164,7 +164,7 @@
   <Target Name="_PrepareNativeAssemblySources"
       Condition=" '$(_AndroidRuntime)' != 'NativeAOT' "
       Inputs="@(_BuildTargetAbis)"
-      Outputs="@(_BuildTargetAbis->'$(_NativeAssemblySourceDir)typemaps.%(Identity).ll')">
+      Outputs="@(_BuildTargetAbis->'$(_NativeAssemblySourceDir)typemap.%(Identity).ll')">
     <ItemGroup>
       <_TypeMapStubAbis Include="@(_BuildTargetAbis)" />
     </ItemGroup>