[Bug #18890] Suppress warnings and fix the message

```
test/ruby/test_parse.rb:1384: warning: assigned but unused variable - obj
test/ruby/test_pattern_matching.rb:1162: warning: unused literal ignored
test/ruby/test_pattern_matching.rb:1165: warning: unused literal ignored
test/ruby/test_pattern_matching.rb:1161: warning: assigned but unused variable - a
test/ruby/test_pattern_matching.rb:1164: warning: assigned but unused variable - b
```

And a newline should be significant here.

1 files changed, 13 insertions, 6 deletions

diff --git a/test/ruby/test_pattern_matching.rb b/test/ruby/test_pattern_matching.rb
index b8c445c806..36731e14f9 100644
--- a/test/ruby/test_pattern_matching.rb
+++ b/test/ruby/test_pattern_matching.rb
@@ -1155,19 +1155,26 @@ END
       end
     end
 
-    [{a: 42}, {b: 42}].each do |i|
-      assert_block('newline should be insignificant after pattern label') do
+    bug18890 = assert_warning(/(?:.*:[47]: warning: unused literal ignored\n){2}/) do
+      eval("#{<<~';;;'}")
+      proc do |i|
         case i
         in a:
-          0
-          true
+          0 # line 4
+          a
         in "b":
-          0
-          true
+          0 # line 7
+          b
         else
           false
         end
       end
+      ;;;
+    end
+    [{a: 42}, {b: 42}].each do |i|
+      assert_block('newline should be significant after pattern label') do
+        bug18890.call(i)
+      end
     end
 
     assert_syntax_error(%q{