Check for name when searching Companion.serializer() function to generate

Name check was forgotten during refactoring, so any user function with
matching signature could be overwritten by the plugin, while correct
function would not have body.

#KT-55682 Fixed

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationFirBlackBoxTestGenerated.java

@@ -158,6 +158,12 @@ public class SerializationFirBlackBoxTestGenerated extends AbstractSerialization
         public void testUseSerializersChain() throws Exception {
             runTest("plugins/kotlinx-serialization/testData/boxIr/useSerializersChain.kt");
         }
+
+        @Test
+        @TestMetadata("userDefinedSerializerInCompanion.kt")
+        public void testUserDefinedSerializerInCompanion() throws Exception {
+            runTest("plugins/kotlinx-serialization/testData/boxIr/userDefinedSerializerInCompanion.kt");
+        }
     }
 
     @Nested

plugins/kotlinx-serialization/tests-gen/org/jetbrains/kotlinx/serialization/runners/SerializationIrBoxTestGenerated.java

@@ -156,4 +156,10 @@ public class SerializationIrBoxTestGenerated extends AbstractSerializationIrBoxT
     public void testUseSerializersChain() throws Exception {
         runTest("plugins/kotlinx-serialization/testData/boxIr/useSerializersChain.kt");
     }
+
+    @Test
+    @TestMetadata("userDefinedSerializerInCompanion.kt")
+    public void testUserDefinedSerializerInCompanion() throws Exception {
+        runTest("plugins/kotlinx-serialization/testData/boxIr/userDefinedSerializerInCompanion.kt");
+    }
 }