[MRG] Fix two temporary files output locations in tests

[luizirber]

There are two tests generating files outside the temporary directory...

Checklist

• Is it mergeable?
• make test Did it pass the tests?
• make coverage Is the new code covered?
• Did it change the command-line interface? Only additions are allowed
  without a major version increment. Changing file formats also requires a
  major version number increment.
• Was a spellchecker run on the source code and documentation after
  changes were made?

[luizirber]

Ready for review and merge @ctb

[codecov]

Codecov Report

Merging #989 into master will increase coverage by 12.17%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master     #989       +/-   ##
===========================================
+ Coverage   80.05%   92.23%   +12.17%     
===========================================
  Files          97       72       -25     
  Lines        7887     5368     -2519     
===========================================
- Hits         6314     4951     -1363     
+ Misses       1573      417     -1156     

Flag	Coverage Δ
#rusttests	?

Impacted Files	Coverage Δ
src/core/src/wasm.rs
src/core/src/ffi/utils.rs
src/core/src/signature.rs
src/core/src/sketch/ukhs.rs
src/core/src/ffi/mod.rs
src/core/src/ffi/signature.rs
src/core/src/sketch/nodegraph.rs
src/core/src/ffi/cmd/compute.rs
src/core/src/sketch/minhash.rs
src/core/src/index/storage.rs
... and 15 more

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