[Test] modify test_download_with_rename_sanitised

With RFC2045 specification, Content-Disposition filenames
parameter containing slash (directory separator) must be
quoted, so changing as such.

deluge/tests/test_httpdownloader.py

@@ -206,7 +206,7 @@ async def test_download_with_rename_exists(self):
         self.assert_contains(filename, 'This file should be called renamed')
 
     async def test_download_with_rename_sanitised(self):
-        url = self.get_url('rename?filename=/etc/passwd')
+        url = self.get_url('rename?filename="/etc/passwd"')
         filename = await download_file(url, fname('original'))
         assert filename == fname('passwd')
         self.assert_contains(filename, 'This file should be called /etc/passwd')