build: drop python 3.8

[tlambert03]

it's EOL

[codecov]

Codecov Report

Attention: Patch coverage is 97.87234% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.89%. Comparing base (ede3511) to head (ee59d27).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/useq/_plot.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #205      +/-   ##
==========================================
+ Coverage   93.87%   93.89%   +0.02%     
==========================================
  Files          18       18              
  Lines        1257     1262       +5     
==========================================
+ Hits         1180     1185       +5     
  Misses         77       77              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

---

🚨 Try these New Features:

• Flaky Tests Detection - Detect and resolve failed and flaky tests