Exclude Guardian testing against Django master

[carltongibson]

Fixes #3406

Excluding Django Guardian clears up the test run against Django master

3 failed, 287 passed, 2 warnings, 456 error in 220.90 seconds

vs

1 failed, 735 passed, 10 skipped, 2 warnings in 7.39 seconds

• Made against v3.3 branch.
• Easy enough to re-add when Guardian fixes this.
• There's probably some neater way of specifying the exclude in tox config — but I couldn't think of it offhand.

[tomchristie]

Wonderful!

[carltongibson]

@tomchristie Glad you like it. :)

[tomchristie]

The failure there should be easy enough to resolve - something on ModelSerializer is being mapped slightly diff between versions. Would be good to fully see the diff between the actual repr() and the expected repr()

[carltongibson]

Yes — at least the output of the run is short enough to look at sensibly here. I'll create a new issue for that.

[xordoquy]

👍 nice job