Create banner for PyCon US

[dragid10]

Once Jay's PyCon US blog post is published, update the /pycon redirect to point to it instead of /events.html.

Files to update

• pycon.html — change the redirect URL (marked with a TODO comment)
• tests/test.py — update test_pycon_redirects_to_events assertion to match the new URL

Context

• PR Add PyCon US homepage banner and /pycon redirect #908 added the redirect pointing to /events.html as a temporary target
• Jay is writing a blog post with PyCon US schedule details that will be the permanent destination