Improve tests for small UTF regex with case fold.

Co-authored-by: Nobuyoshi Nakada <[email protected]>

Author: mrzasa

test/ruby/test_regexp.rb

@@ -2118,13 +2118,10 @@ def test_linear_performance
   def test_bug_16145_caseinsensitive_small_utf # [Bug#16145]
     o_acute_lower = 243.chr('UTF-8')
     o_acute_upper = 211.chr('UTF-8')
-    # [xó] =~ "abcÓ"
-    assert(/[x#{o_acute_lower}]/i.match?("abc#{o_acute_upper}"), "should match o acute case insensitive")
-
+    assert_match(/[x#{o_acute_lower}]/i, "abc#{o_acute_upper}", "should match o acute case insensitive")
 
     e_acute_lower = 233.chr('UTF-8')
     e_acute_upper = 201.chr('UTF-8')
-    # [xé] =~ 'CAFÉ'
-    assert(/[x#{e_acute_lower}]/i.match?("CAF#{e_acute_upper}"), "should match e acute case insensitive")
+    assert_match(/[x#{e_acute_lower}]/i, "CAF#{e_acute_upper}", "should match e acute case insensitive")
   end
 end