Minor modification for the new Gmsh example

[mnagaso]

As following the instruction in the last PR
#1204 (comment)

I modified:

• the name of example directory
• use the nummaterial_velocity_file

Thank you very much for your feedback and merging this PR.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b735263) 54.64% compared to head (998f97e) 53.22%.

Additional details and impacted files

@@            Coverage Diff             @@
##            devel    #1205      +/-   ##
==========================================
- Coverage   54.64%   53.22%   -1.42%     
==========================================
  Files         164      164              
  Lines       30233    30084     -149     
==========================================
- Hits        16520    16012     -508     
- Misses      13713    14072     +359     

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[mnagaso]

Thank you very much for pointing out the problem! I will modify it very soon.