Fix issue where the ImageRenderer's GL context wasn't released

[abey79]

Description

This caused an issue when running the test suite, which could involve creating multiple hundreds of context, ultimately leading to a crash.

More info: moderngl/moderngl#575

Excluded poetry version 1.4.1 due to validation issue with some packages, see python-poetry/poetry#7686 and pradyunsg/furo#639

Checklist

• feature/fix implemented
• code formatting ok (black and isort)
• mypy returns no error
• tests added/updated and pytest succeeds
• documentation added/updated
  • command docstring and option/argument help
  • README.md updated (Feature Overview)
  • CHANGELOG.md updated
  • added new command to reference.rst
  • RTD doc updated and building with no error (make clean && make html in docs/)

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (7106a71) 94.77% compared to head (0921636) 94.77%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #616   +/-   ##
=======================================
  Coverage   94.77%   94.77%           
=======================================
  Files          62       62           
  Lines        5719     5721    +2     
  Branches     1304     1304           
=======================================
+ Hits         5420     5422    +2     
  Misses        182      182           
  Partials      117      117           

Impacted Files	Coverage Δ
vpype_viewer/image/__init__.py	100.00% <100.00%> (ø)

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication