Remove: 移除 Python 3.7 支持

[yanyongyu]

fix #1124

[codecov]

Codecov Report

Merging #1148 (099ebb6) into master (675e70f) will increase coverage by 0.40%.
The diff coverage is 82.02%.

@@            Coverage Diff             @@
##           master    #1148      +/-   ##
==========================================
+ Coverage   78.62%   79.02%   +0.40%     
==========================================
  Files          41       41              
  Lines        3162     3171       +9     
==========================================
+ Hits         2486     2506      +20     
+ Misses        676      665      -11     

Flag	Coverage Δ
unittests	79.02% <82.02%> (+0.40%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
nonebot/internal/adapter/bot.py	45.58% <33.33%> (+0.51%)	⬆️
nonebot/utils.py	86.36% <66.66%> (-1.45%)	⬇️
nonebot/internal/matcher.py	93.70% <71.42%> (-2.64%)	⬇️
nonebot/message.py	39.83% <71.42%> (+1.37%)	⬆️
nonebot/dependencies/__init__.py	90.21% <77.77%> (+0.85%)	⬆️
nonebot/__init__.py	100.00% <100.00%> (ø)
nonebot/consts.py	100.00% <100.00%> (ø)
nonebot/dependencies/utils.py	88.88% <100.00%> (-0.40%)	⬇️
nonebot/drivers/_block_driver.py	38.94% <100.00%> (+5.61%)	⬆️
nonebot/drivers/fastapi.py	88.43% <100.00%> (+1.10%)	⬆️
... and 11 more

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[github-actions]

🚀 Deployed on https://deploy-preview-1148--nonebot2.netlify.app

[XZhouQD]

Good to go as a pure upgrade to abandon python 3.7.x support