Fix generate_decimal128_case in integration test

[viirya]

Which issue does this PR close?

Closes #1439.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #1440 (ac102ca) into master (729934c) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1440      +/-   ##
==========================================
- Coverage   82.67%   82.67%   -0.01%     
==========================================
  Files         185      185              
  Lines       53822    53830       +8     
==========================================
+ Hits        44500    44503       +3     
- Misses       9322     9327       +5     

Impacted Files	Coverage Δ
integration-testing/src/lib.rs	0.00% <0.00%> (ø)
arrow/src/array/transform/mod.rs	86.31% <0.00%> (ø)
parquet_derive/src/parquet_field.rs	66.21% <0.00%> (+0.22%)	⬆️
arrow/src/datatypes/field.rs	54.10% <0.00%> (+0.30%)	⬆️
arrow/src/datatypes/datatype.rs	66.80% <0.00%> (+0.39%)	⬆️

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[liukun4515]

Thanks @viirya

[viirya]

Thanks @liukun4515 !

[alamb]

Looks good to me -- thanks @viirya

[viirya]

Thanks @alamb ! I will continue fixing other integration test failures.