Increase CI kubernetes memory limit to 20Gi to avoid OOM

[ambushwork]

What does this PR do?

Increase CI kubernetes memory limit to 20Gi .

Motivation

To avoid test:plugin task triggering OOM on CI

Additional Notes

The previous fix of adding the override of gradle.properties is revoked.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.68%. Comparing base (11e01a4) to head (d4bb1a2).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@              Coverage Diff              @@
##             develop     #318      +/-   ##
=============================================
- Coverage      78.00%   77.68%   -0.32%     
+ Complexity       260      258       -2     
=============================================
  Files             31       31              
  Lines            941      941              
  Branches         113      113              
=============================================
- Hits             734      731       -3     
- Misses           151      153       +2     
- Partials          56       57       +1     

see 3 files with indirect coverage changes