fix implementation of ConceptPropertyValue.getLang + add test

[osma]

Reasons for creating this PR

PR #1466 introduced a bug that causes infinite recursion in ConceptPropertyValue.getLang. This PR fixes the bug and adds a test that exercises the method.

Link to relevant issue(s), if any

• follow-up fix to Added Symfony translation component #1466

Description of the changes in this PR

• implement getLang by calling the corresponding Model
• add unit test

Known problems or uncertainties in this PR

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)

[sonarcloud]

SonarCloud Quality Gate failed.   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

No Coverage information
0.0% Duplication

Catch issues before they fail your Quality Gate with our IDE extension SonarLint

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.04% 🎉

Comparison is base (76def2f) 70.05% compared to head (c9be91b) 70.09%.

Additional details and impacted files

@@               Coverage Diff               @@
##             skosmos-3    #1507      +/-   ##
===============================================
+ Coverage        70.05%   70.09%   +0.04%     
  Complexity        1641     1641              
===============================================
  Files               32       32              
  Lines             4301     4301              
===============================================
+ Hits              3013     3015       +2     
+ Misses            1288     1286       -2     

Files Changed	Coverage Δ
src/model/ConceptPropertyValue.php	89.02% <100.00%> (+2.43%)	⬆️

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