refactor(exporter-prometheus): promisify prometheus tests

[legendecas]

Which problem is this PR solving?

Promisify prometheus tests and avoid zalgo problem with the constructor callback.

Short description of the changes

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Promisified tests

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

Merging #4431 (27ca563) into main (df63272) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 27ca563 differs from pull request most recent head acd1e42. Consider uploading reports for the commit acd1e42 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4431      +/-   ##
==========================================
- Coverage   92.22%   92.22%   -0.01%     
==========================================
  Files         336      336              
  Lines        9521     9516       -5     
  Branches     2017     2018       +1     
==========================================
- Hits         8781     8776       -5     
  Misses        740      740              

Files	Coverage Δ
...etry-exporter-prometheus/src/PrometheusExporter.ts	96.29% <100.00%> (+0.04%)	⬆️

... and 3 files with indirect coverage changes