Fix bug where truncated normal was not truncated

[dafeda]

(cherry picked from commit d54ed18)

Issue
Resolves #my_issue

Approach
Short description of the approach

(Screenshot of new behavior in GUI if applicable)

Pre review checklist

• Read through the code changes carefully after finishing work
• Make sure tests pass locally (after every commit!)
• Prepare changes in small commits for more convenient review (optional)
• PR title captures the intent of the changes, and is fitting for release notes.
• Updated documentation
• Ensured that unit tests are added for all new behavior (See
  Ground Rules),
  and changes to existing code have good test coverage.

Pre merge checklist

• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.

[xjules]

🚀

[codecov-commenter]

Codecov Report

Merging #6110 (5d4f9a7) into version-6.0 (3df5ab7) will decrease coverage by 0.02%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           version-6.0    #6110      +/-   ##
===============================================
- Coverage        81.94%   81.93%   -0.02%     
===============================================
  Files              350      350              
  Lines            21817    21816       -1     
  Branches           737      737              
===============================================
- Hits             17879    17874       -5     
- Misses            3685     3689       +4     
  Partials           253      253              

Files Changed	Coverage Δ
src/ert/config/gen_kw_config.py	97.89% <100.00%> (-0.02%)	⬇️

... and 1 file with indirect coverage changes

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