Removes fmt from tests.

[francocipollone]

🎉 New feature

Closes #566
Related to #564

Summary

• Removes fmt usage in the tests suite.

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if it affects the public API)

[codecov]

Codecov Report

Merging #563 (0a8a4a9) into main (33cfe38) will increase coverage by 0.03%.
Report is 1 commits behind head on main.
The diff coverage is n/a.

❗ Current head 0a8a4a9 differs from pull request most recent head dc89254. Consider uploading reports for the commit dc89254 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #563      +/-   ##
==========================================
+ Coverage   43.99%   44.03%   +0.03%     
==========================================
  Files         164      164              
  Lines        5423     5423              
  Branches     2890     2890              
==========================================
+ Hits         2386     2388       +2     
+ Misses       1532     1531       -1     
+ Partials     1505     1504       -1     

Files Changed	Coverage Δ
include/maliput/routing/phase.h	0.00% <ø> (ø)
include/maliput/routing/route.h	50.00% <ø> (ø)
src/routing/route.cc	80.76% <ø> (ø)

... and 1 file with indirect coverage changes

[stonier]

LGTM