Getting an exception when reporting about a different exception is not helpful.
On Python 3.11 this is needed for some HTTPErrors.

For DummyTraceback we need tb_lasti.
For DummyFrame we need co_positions.
See https://docs.python.org/3/reference/datamodel.html#traceback-objects
and https://docs.python.org/3/reference/datamodel.html#codeobject.co_positions

$ python2.7 -c 'syntax error'
  File "<string>", line 1
    syntax error
               ^
SyntaxError: invalid syntax
$ python3.6 -c 'syntax error'
  File "<string>", line 1
    syntax error
               ^
SyntaxError: invalid syntax
$ python3.8 -c 'syntax error'
  File "<string>", line 1
    syntax error
           ^
SyntaxError: invalid syntax
$ python3.9 -c 'syntax error'
  File "<string>", line 1
    syntax error
           ^
SyntaxError: invalid syntax
$ python3.10 -c 'syntax error'
  File "<string>", line 1
    syntax error
           ^^^^^
SyntaxError: invalid syntax

* Add official support for Python 3.9.
* Undo dropping support for Python 3.5.
* Drop support for running the tests using `python setup.py test`.

Co-authored-by: Marius Gedminas <marius@gedmin.as>

* Adapt tests to Python 3.9.
* Drop support for Python 3.5 as its sunset is in some months.