chore: re-enable instrumentation-fastify unit test on node@18

[chigia001]

Which problem is this PR solving?

• I test multiple time on my local node@18 and instrumentation-fastify seem working fine with node@18, so we might want to enable this test again.

Short description of the changes

• remove instrumentation-fastify from the ignore list of node@18 unit test

[codecov]

Codecov Report

Merging #1568 (968bcda) into main (84a2377) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1568   +/-   ##
=======================================
  Coverage   96.06%   96.06%           
=======================================
  Files          14       14           
  Lines         914      914           
  Branches      199      199           
=======================================
  Hits          878      878           
  Misses         36       36           

[pichlermarc]

Thanks 🙂