ARROW-11881: [Rust][DataFusion] Fix clippy lint

[alamb]

ARROW-11881: [Rust][DataFusion] Fix clippy lint

A linter error has appeared on master somehow:

error: unnecessary parentheses around `for` iterator expression
--> datafusion/src/physical_plan/merge.rs:124:31
|
124 | for part_i in (0..input_partitions) {
| ^^^^^^^^^^^^^^^^^^^^^ help: remove these parentheses
|
= note: `-D unused-parens` implied by `-D warnings`

Seen on at least #9612 and #9639:

https://github.com/apache/arrow/pull/9612/checks?check_run_id=2042047472

https://github.com/apache/arrow/pull/9639/checks?check_run_id=2042649120

[github-actions]

https://issues.apache.org/jira/browse/ARROW-11881

[codecov-io]

Codecov Report

Merging #9642 (c9bb438) into master (35daca2) will increase coverage by 0.06%.
The diff coverage is 88.18%.

@@ Coverage Diff @@## master #9642 +/- ##
==========================================
+ Coverage 82.32% 82.39% +0.06% 
==========================================
Files 245 245 Lines 56412 57170 +758 ==========================================
+ Hits 46442 47105 +663 - Misses 9970 10065 +95 

Impacted Files	Coverage Δ
rust/benchmarks/src/bin/tpch.rs	38.33% <ø> (ø)
...datafusion/src/physical_plan/crypto_expressions.rs	52.45% <ø> (ø)
rust/datafusion/src/physical_plan/mod.rs	88.00% <ø> (ø)
rust/arrow/src/datatypes/field.rs	55.47% <47.61%> (-0.66%)	⬇️
rust/datafusion/src/physical_plan/parquet.rs	87.83% <57.14%> (-0.22%)	⬇️
...datafusion/src/physical_plan/string_expressions.rs	73.38% <74.59%> (-3.62%)	⬇️
rust/datafusion/src/physical_plan/hash_join.rs	84.16% <77.77%> (+0.64%)	⬆️
rust/arrow/src/datatypes/schema.rs	73.39% <78.57%> (+0.76%)	⬆️
rust/datafusion/src/physical_plan/repartition.rs	81.21% <87.50%> (-0.14%)	⬇️
rust/datafusion/src/physical_plan/functions.rs	89.22% <96.19%> (+3.70%)	⬆️
... and 13 more

---

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[Dandandan]

LGTM

[alamb]

Thanks @nevi-me and @Dandandan

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.39%. Comparing base (35daca2) to head (c9bb438).

Additional details and impacted files

@@ Coverage Diff @@## master #9642 +/- ##
==========================================
+ Coverage 82.32% 82.39% +0.06% 
==========================================
Files 245 245 Lines 56412 57170 +758 ==========================================
+ Hits 46442 47105 +663 - Misses 9970 10065 +95 

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