RFC: Drop python 39

[jenshnielsen]

Most of the scientific python stack has adopted SPEC 0 which means that python 3.9 support should be dropped from late 2023. As an example we can see in #5602 that Ipython has dropped support for 3.9.

This is to propose that QCoDeS also drops support for 3.9

• This should also update the readme
• Remove 3.9 ci jobs

[codecov]

Codecov Report

Merging #5620 (92df777) into main (150d405) will decrease coverage by 0.04%.
The diff coverage is 85.93%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5620      +/-   ##
==========================================
- Coverage   66.39%   66.36%   -0.04%     
==========================================
  Files         354      354              
  Lines       30965    30964       -1     
==========================================
- Hits        20560    20549      -11     
- Misses      10405    10415      +10     

[codecov]

Codecov Report

Attention: Patch coverage is 86.74352% with 46 lines in your changes are missing coverage. Please review.

Project coverage is 67.52%. Comparing base (58ee206) to head (2cff640).

Files	Patch %	Lines
src/qcodes/instrument_drivers/Galil/dmc_41x3.py	7.69%	12 Missing ⚠️
..._drivers/AlazarTech/ATS_acquisition_controllers.py	25.00%	3 Missing ⚠️
...ent_drivers/signal_hound/SignalHound_USB_SA124B.py	57.14%	3 Missing ⚠️
src/qcodes/instrument_drivers/Keysight/KtMAwg.py	50.00%	2 Missing ⚠️
...ent_drivers/QuantumDesign/DynaCoolPPMS/DynaCool.py	60.00%	2 Missing ⚠️
...rc/qcodes/instrument_drivers/rigol/Rigol_DG1062.py	50.00%	2 Missing ⚠️
src/qcodes/instrument_drivers/tektronix/AWG5014.py	71.42%	2 Missing ⚠️
...odes/instrument_drivers/tektronix/AWGFileParser.py	50.00%	2 Missing ⚠️
src/qcodes/instrument_drivers/yokogawa/GS200.py	33.33%	2 Missing ⚠️
...odes/instrument_drivers/Keithley/Keithley_3706A.py	90.90%	1 Missing ⚠️
... and 15 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5620      +/-   ##
==========================================
- Coverage   67.55%   67.52%   -0.03%     
==========================================
  Files         351      351              
  Lines       30492    30480      -12     
==========================================
- Hits        20598    20582      -16     
- Misses       9894     9898       +4     

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[astafan8]

exciting :) and removing 3.9 ci and updating readme is still todo