[IR][tests] Update tests to reflect changes in partial linkage error messages

compiler/testData/klibABI/removeAbstractFunctionFromAbstractClass/main/m.kt

@@ -4,16 +4,23 @@ import lib2.B
 fun box(): String {
     val a: A = B()
 
-    try {
+    return try {
         val answer: Int = a.foo() // <-- should throw linkage error here
         println(answer)
+        "FAIL"
     } catch (e: Throwable) {
-        if (e.isLinkageError("lib2.B.foo")) return "OK"
+        e.checkLinkageError("foo", "B")
     }
-
-    return "FAIL"
 }
 
-private fun Throwable.isLinkageError(symbolName: String): Boolean =
-    this::class.simpleName == "IrLinkageError"
-            && message == "Abstract function $symbolName is not implemented in non-abstract class ${symbolName.substringBeforeLast(".")}"
+private fun Throwable.checkLinkageError(symbolName: String, className: String): String {
+    if (this::class.simpleName != "IrLinkageError") return "Unexpected throwable: ${this::class}"
+
+    val expectedMessage = "Abstract function $symbolName is not implemented in non-abstract class $className"
+    val actualMessage = message.orEmpty()
+
+    return if (expectedMessage == actualMessage)
+        "OK"
+    else
+        "EXPECTED: $expectedMessage, ACTUAL: $actualMessage"
+}