Add test for obsolete issue

#KT-38420 Obsolete

compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt38420.kt

@@ -0,0 +1,10 @@
+// !USE_EXPERIMENTAL: kotlin.RequiresOptIn
+
+@OptIn(ExperimentalStdlibApi::class)
+val list: List<String> = buildList {
+    val inner: List<String> = maybe() ?: emptyList()
+
+    addAll(inner)
+}
+
+fun maybe(): List<String>? = null

compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt38420.txt

@@ -0,0 +1,4 @@
+package
+
+@kotlin.OptIn(markerClass = {kotlin.ExperimentalStdlibApi::class}) public val list: kotlin.collections.List<kotlin.String>
+public fun maybe(): kotlin.collections.List<kotlin.String>?

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestWithStdLibGenerated.java

@@ -2037,6 +2037,11 @@ public class DiagnosticsTestWithStdLibGenerated extends AbstractDiagnosticsTestW
                 runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt36220.kt");
             }
 
+            @TestMetadata("kt38420.kt")
+            public void testKt38420() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt38420.kt");
+            }
+
             @TestMetadata("nestedLambdaInferenceWithListMap.kt")
             public void testNestedLambdaInferenceWithListMap() throws Exception {
                 runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/nestedLambdaInferenceWithListMap.kt");

compiler/tests/org/jetbrains/kotlin/checkers/javac/DiagnosticsTestWithStdLibUsingJavacGenerated.java

@@ -2037,6 +2037,11 @@ public class DiagnosticsTestWithStdLibUsingJavacGenerated extends AbstractDiagno
                 runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt36220.kt");
             }
 
+            @TestMetadata("kt38420.kt")
+            public void testKt38420() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/kt38420.kt");
+            }
+
             @TestMetadata("nestedLambdaInferenceWithListMap.kt")
             public void testNestedLambdaInferenceWithListMap() throws Exception {
                 runTest("compiler/testData/diagnostics/testsWithStdLib/coroutines/inference/nestedLambdaInferenceWithListMap.kt");