Uploads fail from Cirrus-CI with 400 error

[slact]

This change appears to have broken uploading from Cirrus-CI. Previously, the output was

bash <(curl -s https://codecov.io/bash)
  _____          _
 / ____|        | |
| |     ___   __| | ___  ___ _____   __
| |    / _ \ / _` |/ _ \/ __/ _ \ \ / /
| |___| (_) | (_| |  __/ (_| (_) \ V /
 \_____\___/ \__,_|\___|\___\___/ \_/
                              Bash-8a28df4
x> No CI provider detected.
    Testing inside Docker? http://docs.codecov.io/docs/testing-with-docker
    Testing with Tox? https://docs.codecov.io/docs/python#section-testing-with-tox
    project root: .
--> token set from env
    Yaml found at: .codecov.yml
[...]
==> Uploading reports
    url: https://codecov.io
    query: branch=master&commit=[...]&build=&build_url=&name=&tag=&slug=[...]&service=&flags=&pr=&job=
    -> Pinging Codecov
https://codecov.io/upload/v4?package=bash-8a28df4&token=secret&branch=master&commit=[...]&build=&build_url=&name=&tag=&slug=[...]&service=&flags=&pr=&job=
    -> Uploading
    -> View reports at https://codecov.io/[...]

That is, even though the CI provider was not detected, the upload completed successfully.

Now, this happens instead:

bash <(curl -s https://codecov.io/bash)
  _____          _
 / ____|        | |
| |     ___   __| | ___  ___ _____   __
| |    / _ \ / _` |/ _ \/ __/ _ \ \ / /
| |___| (_) | (_| |  __/ (_| (_) \ V /
 \_____\___/ \__,_|\___|\___\___/ \_/
                              Bash-20191120-4983e44
==> Cirrus CI detected.
    project root: .
--> token set from env
    Yaml found at: .codecov.yml
[...]
==> Uploading reports
    url: https://codecov.io
    query: branch=master&commit=[...]&build=[...]&build_url=&name=&tag=&slug=[...]&service=cirrus&flags=&pr=&job=linux
    -> Pinging Codecov
https://codecov.io/upload/v4?package=bash-20191120-4983e44&token=secret&branch=master&commit=[...]&build=[...]&build_url=&name=&tag=&slug=[...]&service=cirrus&flags=&pr=&job=linux
    -> Uploading
    X> Failed to upload
    -> Sleeping for 30s and trying again...
    -> Pinging Codecov
https://codecov.io/upload/v4?package=bash-20191120-4983e44&token=secret&branch=master&commit=[...]&build=[...]&build_url=&name=&tag=&slug=[...]&service=cirrus&flags=&pr=&job=linux
    -> Uploading
    X> Failed to upload
    -> Sleeping for 30s and trying again...
    -> Pinging Codecov
https://codecov.io/upload/v4?package=bash-20191120-4983e44&token=secret&branch=master&commit=[...]&build=[...]&build_url=&name=&tag=&slug=[...]&service=cirrus&flags=&pr=&job=linux
    -> Uploading
    X> Failed to upload
    -> Sleeping for 30s and trying again...
    -> Pinging Codecov
https://codecov.io/upload/v4?package=bash-20191120-4983e44&token=secret&branch=master&commit=[...]&build=[...]&build_url=&name=&tag=&slug=[...]&service=cirrus&flags=&pr=&job=linux
    -> Uploading
    X> Failed to upload
    -> Sleeping for 30s and trying again...
    -> Uploading to Codecov
    HTTP 400
service must be ci-provider

This appears to have started about 8 days ago. running the bash script after export CIRRUS_CI="" work again, so the backend is clearly refusing to accept the cirrus service.