Investigate potential problems with incremental builds

We have a flaky build test:
```

1) at Xamarin.Android.Build.Tests.IncrementalBuildTest.BasicApplicationRepetitiveBuild(AndroidRuntime runtime) in /Users/cloudtest/vss/_work/1/s/android/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/IncrementalBuildTest.cs:line 36

Standard Output Messages:
[TESTLOG] Test BasicApplicationRepetitiveBuildCoreCLR Starting
D:\a\_work\1\s\bin\Release\dotnet\dotnet build D:\a\_work\1\a\TestRelease\06-29_03.33.43\temp\BasicApplicationRepetitiveBuildCoreCLR\UnnamedProject.csproj /t:Build,SignAndroidPackage /noconsolelogger "/flp1:LogFile=D:\a\_work\1\a\TestRelease\06-29_03.33.43\temp\BasicApplicationRepetitiveBuildCoreCLR\build.log;Encoding=UTF-8;Verbosity=normal" -nodeReuse:false @"D:\a\_work\1\a\TestRelease\06-29_03.33.43\temp\BasicApplicationRepetitiveBuildCoreCLR\project.rsp"
Found Time Elapsed 00:00:49.4500000
D:\a\_work\1\s\bin\Release\dotnet\dotnet build D:\a\_work\1\a\TestRelease\06-29_03.33.43\temp\BasicApplicationRepetitiveBuildCoreCLR\UnnamedProject.csproj /t:Build,SignAndroidPackage /noconsolelogger "/flp1:LogFile=D:\a\_work\1\a\TestRelease\06-29_03.33.43\temp\BasicApplicationRepetitiveBuildCoreCLR\build.log;Encoding=UTF-8;Verbosity=normal" -nodeReuse:false @"D:\a\_work\1\a\TestRelease\06-29_03.33.43\temp\BasicApplicationRepetitiveBuildCoreCLR\project.rsp"
Found Time Elapsed 00:01:19.4700000
[TESTLOG] Test BasicApplicationRepetitiveBuildCoreCLR Complete
[TESTLOG] Test BasicApplicationRepetitiveBuildCoreCLR Outcome=Failed
```

The second build should be faster than the first build, but it's significantly slower. This can be due to several reasons:
- we have a bug in our incremental builds and the build is not incremental really
- the test machine was being slow/overloaded during this test for all sorts of reasons and that made the test fail and the test failure is misleading

We should disable the test for the time being and investigate if we regressed incrementality or what is actually going on.