Update to linopy v0.2

[FabianHofmann]

EDIT:

• Extended feature: Support quadratic cost terms for generators.
• Python 3.8 support was dropped

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• Newly introduced dependencies are added to environment.yaml, environment_docs.yaml and setup.py (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

[codecov]

Codecov Report

Patch coverage: 72.72% and project coverage change: -0.05 ⚠️

Comparison is base (5cb14d0) 77.19% compared to head (3124472) 77.14%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #653      +/-   ##
==========================================
- Coverage   77.19%   77.14%   -0.05%     
==========================================
  Files          27       27              
  Lines        6511     6524      +13     
  Branches     1378     1384       +6     
==========================================
+ Hits         5026     5033       +7     
- Misses       1194     1198       +4     
- Partials      291      293       +2     

Impacted Files	Coverage Δ
pypsa/optimization/optimize.py	86.69% <64.70%> (-1.48%)	⬇️
pypsa/optimization/constraints.py	90.93% <100.00%> (-0.07%)	⬇️

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