[tests] Import Configuration.props in Mono.Android-Test.Library (#3320)

Context: e956107
Context: #3305

When `Mono.Android-Test.Library.csproj` was added in e956107 it did
not import our `Configuration.props` file which contains default
paths to the Android tooling that we provision.  This recently caused
a breakage when bumping the `$(TargetFrameworkVersion)` of this
project to v10.0 (within PR #3305) and building against a system
install of XA, as the Android SDK path which was automatically
resolved did not contain `platforms/android-29/android.jar`.

Importing `Configuration.props` file should fix this build failure.

Author: pjcollins

src/Mono.Android/Test/Mono.Android-Test.Library/Mono.Android-Test.Library.csproj

@@ -17,6 +17,7 @@
     <GenerateSerializationAssemblies>Off</GenerateSerializationAssemblies>
     <TargetFrameworkVersion>v10.0</TargetFrameworkVersion>
   </PropertyGroup>
+  <Import Project="..\..\..\..\Configuration.props" />
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
     <DebugType>portable</DebugType>