[Backport 2.x] Fix constant_keyword field type not working

[kkewwei]

Backport a252b29 from #14807

[github-actions]

❌ Gradle check result for dc7f92b: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

✅ Gradle check result for dc7f92b: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.59%. Comparing base (39da9bd) to head (dc7f92b).
Report is 2 commits behind head on 2.x.

Additional details and impacted files

@@             Coverage Diff              @@
##                2.x   #14946      +/-   ##
============================================
- Coverage     71.66%   71.59%   -0.07%     
- Complexity    62739    62742       +3     
============================================
  Files          5120     5121       +1     
  Lines        294255   294268      +13     
  Branches      42877    42880       +3     
============================================
- Hits         210871   210695     -176     
- Misses        65668    65881     +213     
+ Partials      17716    17692      -24     

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