Multi-language Support: Fix error in CRA sample project

[martin-strecker-sonarsource]

Steps to reproduce

dotnet new react -n CRA
cd CRA
git init
git commit -m "Initial commit"
dotnet build
dotnet E:\dl\SonarScanner.MSBuild.dll begin /k:CRA /d:sonar.host.url=http://localhost:9000 /d:sonar.login=squ_***
dotnet build --no-incremental
dotnet E:\dl\SonarScanner.MSBuild.dll end /d:sonar.login=squ_***

Fails in the end step with

INFO: ------------------------------------------------------------------------
INFO: EXECUTION FAILURE
INFO: ------------------------------------------------------------------------
INFO: Total time: 22.033s
INFO: Final Memory: 16M/96M
ERROR: Error during SonarScanner execution
INFO: ------------------------------------------------------------------------
ERROR: File ClientApp/src/App.test.js can't be indexed twice. Please check that inclusion/exclusion patterns produce disjoint sets for main and test files
ERROR:
The SonarScanner did not complete successfully
16:08:41.095  Post-processing failed. Exit code: 1

Details: #2084 (comment)