make use of exception wrapper in io test

_test/tests/inc/io_replaceinfile.test.php

@@ -101,12 +101,11 @@ class io_replaceinfile_test extends DokuWikiTest {
     function test_badparam()
     {
         if (class_exists('PHPUnit\Framework\Error\Warning')) {
-            // PHPUnit 6
-            $this->expectException(PHPUnit\Framework\Error\Warning::class);
+            $expect = PHPUnit\Framework\Error\Warning::class; // PHPUnit 6
         } else {
-            // PHPUnit 5
-            $this->expectException(PHPUnit_Framework_Error_Warning::class);
+            $expect = PHPUnit_Framework_Error_Warning::class; // PHPUnit 5
         }
+        $this->setExpectedException($expect);
 
         /* The empty $oldline parameter should be caught before the file doesn't exist test. */
         $this->assertFalse(io_replaceInFile(TMP_DIR.'/not_existing_file.txt', '', '', false, 0));