Fix compiler client test after introducing nullable CompilerMessageLocation

libraries/tools/kotlin-compiler-client-embeddable-test/src/test/kotlin/org/jetbrains/kotlin/compiler/client/CompilerClientIT.kt

@@ -111,7 +111,7 @@ internal fun captureOutAndErr(body: () -> Unit): String {
 
 class TestMessageCollector : MessageCollector {
 
-    data class Message(val severity: CompilerMessageSeverity, val message: String, val location: CompilerMessageLocation)
+    data class Message(val severity: CompilerMessageSeverity, val message: String, val location: CompilerMessageLocation?)
 
     val messages = arrayListOf<Message>()
 
@@ -119,7 +119,7 @@ class TestMessageCollector : MessageCollector {
         messages.clear()
     }
 
-    override fun report(severity: CompilerMessageSeverity, message: String, location: CompilerMessageLocation) {
+    override fun report(severity: CompilerMessageSeverity, message: String, location: CompilerMessageLocation?) {
         messages.add(Message(severity, message, location))
     }