Generated by `pyupgrade --py3-plus --keep-percent-format` on all our
Python code except `zthumbor` and `zulip-ec2-configure-interfaces`,
followed by manual indentation fixes.
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
I dug into why we never did this before, and it turns out we did, but
using `$.trim()` (which removes leading whitespace as well!). When
removing the `$.trim()` usage.
Fixes#3294.