Add switch warning test

Author: odersky

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -184,6 +184,7 @@ class CompilationTests extends ParallelTesting {
     compileFile("../tests/neg-custom-args/noimports2.scala", defaultOptions.and("-Yno-imports")) +
     compileFile("../tests/neg-custom-args/overloadsOnAbstractTypes.scala", allowDoubleBindings) +
     compileFile("../tests/neg-custom-args/xfatalWarnings.scala", defaultOptions.and("-Xfatal-warnings")) +
+    compileFile("../tests/neg-custom-args/i3561.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg-custom-args/pureStatement.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg-custom-args/i3589-a.scala", defaultOptions.and("-Xfatal-warnings")) +
     compileFile("../tests/neg-custom-args/i2333.scala", defaultOptions.and("-Xfatal-warnings")) +