ARROW-5753: [Rust] Fix test failure in CI code coverage

[sunchao]

No description provided.

[codecov-io]

Codecov Report

Merging #4748 into master will increase coverage by 0.9%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #4748     +/-   ##
=========================================
+ Coverage   86.44%   87.34%   +0.9%     
=========================================
  Files         992      992             
  Lines      138020   138020             
  Branches     1418     1418             
=========================================
+ Hits       119311   120559   +1248     
+ Misses      18347    17099   -1248     
  Partials      362      362

Impacted Files	Coverage Δ
rust/parquet/src/util/test_common/file_util.rs	76.66% <0%> (-20%)	⬇️
cpp/src/arrow/csv/column-builder.cc	95.29% <0%> (-1.77%)	⬇️
cpp/src/plasma/thirdparty/ae/ae.c	70.75% <0%> (-0.95%)	⬇️
rust/arrow/src/array/array.rs	93.26% <0%> (+0.2%)	⬆️
rust/arrow/src/datatypes.rs	78.63% <0%> (+0.27%)	⬆️
rust/parquet/src/arrow/schema.rs	86.39% <0%> (+0.31%)	⬆️
rust/arrow/src/csv/reader.rs	86.29% <0%> (+2.04%)	⬆️
rust/arrow/src/compute/array_ops.rs	98.12% <0%> (+3.75%)	⬆️
rust/datafusion/src/logicalplan.rs	52.06% <0%> (+5.37%)	⬆️
rust/datafusion/src/sql/planner.rs	74.91% <0%> (+6%)	⬆️
... and 17 more

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[sunchao]

@fsaintjacques @andygrove @nevi-me : could you take a look?

[nevi-me]

LGTM

[kszucs]

LGTM