[AMORO-3940] Flink config load will cause ClassCastException when dir…

[simonsssu]

Close #3940

[klion26]

Thanks for the contribution, could you please add a test to cover this case

[codecov-commenter]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 28.95%. Comparing base (cbdc517) to head (1826537).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
.../amoro/server/manager/FlinkOptimizerContainer.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3941      +/-   ##
============================================
+ Coverage     22.12%   28.95%   +6.82%     
- Complexity     2461     3879    +1418     
============================================
  Files           445      632     +187     
  Lines         40897    50675    +9778     
  Branches       5767     6464     +697     
============================================
+ Hits           9050    14671    +5621     
- Misses        31089    34974    +3885     
- Partials        758     1030     +272     

Flag	Coverage Δ
core	28.95% <50.00%> (?)
trino	?

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