Drop support for Python 3.7

[empicano]

Python 3.7 has reached its end-of-life. Poetry dropped support in 1.6.0 so our test workflow is breaking. @vvanglro made an ad-hoc fix in #245 for that, but I think we're good to go to drop it as well in the next release.

Is there anything we can simplify in the code with this step that I missed?

[codecov]

Codecov Report

Merging #246 (48cc226) into main (b9ce2bf) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #246   +/-   ##
=====================================
  Coverage   84.1%   84.1%           
=====================================
  Files          4       4           
  Lines        468     468           
  Branches      87      87           
=====================================
  Hits         394     394           
  Misses        47      47           
  Partials      27      27           

Files Changed	Coverage Δ
aiomqtt/client.py	82.7% <100.0%> (ø)

[frederikaalund]

Good idea to drop Python 3.7 support! I think that we've done our maintenance duty in that part (most other libraries dropped it already). 😄

Besides the positional-only arguments, we also got the walrus operator (:=) in python 3.8.later. There may be a use case for that somewhere but it's not really worth the refactor IMHO. :)

See my review for details. Let me know if you have any questions! 👍

[JonathanPlasse]

Good work!