Set java home to jdk11 for sonarcloud

[z4kn4fein]

Describe the purpose of your pull request

Sonarcloud scans are failing due to a wrong java version, so this PR points the JAVA_HOME env variable to jdk11.

Requirement checklist (only if applicable)

• [ ] I have covered the applied changes with automated tests.
• [x] I have executed the full automated test set against my changes.
• [x] I have validated my changes against all supported platform versions.
• [x] I have read contributing guidelines.

[codecov[bot]]

Codecov Report

Merging #20 (c700a49) into master (3ec1004) will not change coverage. The diff coverage is n/a.

:exclamation: Current head c700a49 differs from pull request most recent head 2d2cfa0. Consider uploading reports for the commit 2d2cfa0 to get more accurate results

@@           Coverage Diff           @@
##           master      #20   +/-   ##
=======================================
  Coverage   93.57%   93.57%           
=======================================
  Files          27       27           
  Lines         700      700           
  Branches      160      160           
=======================================
  Hits          655      655           
  Misses         12       12           
  Partials       33       33           

Impacted Files	Coverage Δ
src/ConfigCatClient/ConfigCatClient.cs	90.15% <0.00%> (ø)
src/ConfigCatClient/HttpConfigFetcher.cs	90.47% <0.00%> (ø)
src/ConfigCatClient/Evaluate/RolloutEvaluator.cs	95.32% <0.00%> (ø)
...ConfigCatClient/ConfigService/ConfigServiceBase.cs	92.85% <0.00%> (ø)

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