Add flake8-no-implicit-concat

[booniepepper]

What do these changes do?

This will forbid weird implicit string concatenations.

https://pypi.org/project/flake8-no-implicit-concat/

Are there changes in behavior for the user?

Related issue number

Checklist

• [ ] I think the code is well written
• [ ] Unit tests for the changes exist
• [ ] Documentation reflects the changes
• [ ] If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• [ ] Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[booniepepper]

(While a draft: Expecting the first attempt to fail, I'll update accordingly when I can make the time)

[webknjaz]

May I ask you to keep the deps sorted alphabetically?

[Dreamsorcerer]

(While a draft: Expecting the first attempt to fail, I'll update accordingly when I can make the time)

Think you need to enable the codes in the flake8 config. Probably just NIC001 and NIC101 (I'm not sure I want to disallow multi-line concatenations).

[webknjaz]

I'm not sure I want to disallow multi-line concatenations

I'd like to keep multiline implicit concat allowed.

[webknjaz]

@booniepepper this will need a changelog fragment of the contrib type: https://docs.aiohttp.org/en/stable/contributing.html#adding-change-notes-with-your-prs.