Updated async apns timeout to 10s from 1

Updated async apns timeout to 10s from 1

Make mutable-content int (1) instead of bool (True) (jazzband#763)

APNS expect as int in the payload.
Setting `mutable_content` to True, will set `mutable-content` to 1.

Bump actions/cache from 2 to 4

Bumps [actions/cache](https://github.com/actions/cache) from 2 to 4.
- [Release notes](https://github.com/actions/cache/releases)
- [Changelog](https://github.com/actions/cache/blob/main/RELEASES.md)
- [Commits](actions/cache@v2...v4)

---
updated-dependencies:
- dependency-name: actions/cache
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Changed firebase-admin's deprecated send_all method for send_each (ja…

…zzband#715)

Remove python 3.6 support. (jazzband#718)

* Remove python 3.6 support.

* Remove unsupported code

Fixes twine reported warnings when building package. (jazzband#695)

Fixes twine reported warnings when building package. (jazzband#695)

docs: fix codecov badge. (jazzband#651)

Show coverage badge.

registration_id no longer hard-coded in DeviceViewSetMixin

`lookup_field` was declared in `DeviceViewSetMixin` and never used. Instead the create method referred to string literal instead of this field. No the field is used. You can inherit from `DeviceViewSetMixin`, redefined the `lookup_field` and use if with your views instead of having to rewrite the `create` method yourself