Add an additional test with a newline, one that's very similar to…

Add an additional test with a newline, one that's very similar to test_parens_in_expressions, but because the newline is not a literal newline, but a backslash en, this error is triggered.

Lib/test/test_fstring.py

@@ -378,6 +378,7 @@ f'{a * x()}'"""
                              r"rf'{\t3}'",
                              r"rf'{\}'",
                              r"""rf'{"\N{LEFT CURLY BRACKET}"}'""",
+                             r"f'{\n}'",
                              ])
 
     def test_no_escapes_for_braces(self):