doc: replace URL action example with form The example to provide a link to take or resolve an item was broken. Roundup has required a POST not GET for changes to the database for a while. This example was never fixed. Replaced a link using GET with a POSTed form. This changes the activating element from a link to a button. The button could be restyled as a link using CSS I think. The original example was also not canonical. It used :action rather than the canonical @action.

try:
  # used for python2 and python 3 < 3.13
  import cgi as cgi
  from cgi import FieldStorage, MiniFieldStorage
except ImportError:
  # use for python3 >= 3.13
  from roundup.anypy.vendored import cgi
  from roundup.anypy.vendored.cgi import FieldStorage, MiniFieldStorage