Get rid of duplicated file names in spec tests

Otherwise, corresponding IDE tests would fail on creation duplicated
files in the same directory

compiler/tests-spec/testData/diagnostics/linked/expressions/prefix-expressions/prefix-increment-expression/p-4/neg/1.1.kt

@@ -13,7 +13,7 @@
  */
 
 
-// FILE: TestCase.kt
+// FILE: TestCase1.kt
 // TESTCASE NUMBER: 1
 package testPackCase1
 
@@ -36,7 +36,7 @@ class Case1() {
     var a: A = A()
 }
 
-// FILE: TestCase.kt
+// FILE: TestCase2.kt
 // TESTCASE NUMBER: 2
 package testPackCase2