Update dependency flake8-isort to v4

This MR contains the following updates:

Package	Type	Update	Change
flake8-isort	dev-dependencies	major	^3.0.0 -> ^4.0.0

Release Notes retrieval for this MR were skipped because no github.com credentials were available. To add credentials for github.com to your config, please see this guide.

---

Renovate configuration

Schedule: At any time (no schedule defined).

Automerge: Disabled by config. Please merge this manually once you are satisfied.

Rebasing: Whenever MR becomes conflicted, or you tick the rebase/retry checkbox.

Ignore: Close this MR and you won't be reminded about this update again.

---

• If you want to rebase/retry this MR, check this box

---

This MR has been generated by Renovate Bot.

Artifact update problem

Renovate failed to update an artifact related to this branch. You probably do not want to merge this MR as-is.

Renovate will retry this branch, including artifacts, only when one of the following happens:

• any of the package files in this branch needs updating, or
• the branch becomes conflicted, or
• you check the rebase/retry checkbox if found above, or
• you rename this MR's title to start with "rebase!" to trigger it manually

The artifact failure details are included below:

File name: poetry.lock

Creating virtualenv aleksis-app-dashboardfeeds-NJz_phru-py3.8 in /home/ubuntu/.cache/pypoetry/virtualenvs
Updating dependencies
Resolving dependencies...

[ReadError]
file could not be opened successfully

merged

mentioned in commit 7d11ef85