Run 'black' on tui-window.py

Mark pointed out that a recent patch of mine caused the buildbot to
complain about the formatting of some Python test code.  This patch
re-runs 'black' to fix the problem.

gdb/testsuite/gdb.python/tui-window.py

@@ -32,8 +32,10 @@ class TestWindow:
         self.win.erase()
         w = self.win.width
         h = self.win.height
-        self.win.write(string="Test: " + str(self.count) + " " + str(w) + "x" + str(h),
-                       full_window=False)
+        self.win.write(
+            string="Test: " + str(self.count) + " " + str(w) + "x" + str(h),
+            full_window=False,
+        )
         self.count = self.count + 1
 
     # Tries to delete the title attribute.  GDB will throw an error.