terminal: when the skip/xfail is empty, don't show it as "()"

Avoid showing a line like

    x.py::test_4 XPASS ()   [100%]

which looks funny.

Author: bluetech

src/_pytest/terminal.py

@@ -554,7 +554,7 @@ def pytest_runtest_logreport(self, report: TestReport) -> None:
                     )
                     reason = _get_raw_skip_reason(rep)
                     reason_ = _format_trimmed(" ({})", reason, available_width)
-                    if reason_ is not None:
+                    if reason and reason_ is not None:
                         self._tw.write(reason_)
                 if self._show_progress_info:
                     self._write_progress_information_filling_space()

testing/test_terminal.py

@@ -362,6 +362,10 @@ def test_2():
             @pytest.mark.xfail(reason="789")
             def test_3():
                 assert False
+
+            @pytest.mark.xfail(reason="")
+            def test_4():
+                assert False
         """
         )
         result = pytester.runpytest("-v")
@@ -370,6 +374,7 @@ def test_3():
                 "test_verbose_skip_reason.py::test_1 SKIPPED (123) *",
                 "test_verbose_skip_reason.py::test_2 XPASS (456) *",
                 "test_verbose_skip_reason.py::test_3 XFAIL (789) *",
+                "test_verbose_skip_reason.py::test_4 XFAIL  *",
             ]
         )