Moves a clippy attribute

[brooksprumo]

Problem

New clippy nighly has a new warning:

warning: item has both inner and outer attributes
   --> memory-management/src/aligned_memory.rs:209:1
    |
209 | / #[cfg(test)]
210 | | mod tests {
211 | |     #![allow(clippy::arithmetic_side_effects)]
    | |______________________________________________^
    |
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mixed_attributes_style
    = note: `#[warn(clippy::mixed_attributes_style)]` on by default

Summary of Changes

Move the attribute.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.9%. Comparing base (e027a8b) to head (62d8d66).
Report is 18 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff            @@
##           master     #194    +/-   ##
========================================
  Coverage    81.8%    81.9%            
========================================
  Files         838      837     -1     
  Lines      226389   226502   +113     
========================================
+ Hits       185342   185570   +228     
+ Misses      41047    40932   -115