test: Fix missing line coverage when using Node v14

[HW13]

Summary

• For some reason test coverage started dipping under 100%, but only on Node v14 and not v16
  • Currently: https://github.com/autotelic/fastify-opentelemetry/runs/7963898090?check_suite_focus=true#step:5:31
  • Previously: https://github.com/autotelic/fastify-opentelemetry/runs/6891777049?check_suite_focus=true#step:5:30
  • No changes on our part aside from docs update
  • Was able to reproduce locally, but only on Node v14
  • Looks like we missed adding an await to the fastify.register call in our setupTests function
  • Updating this fixed the issue
  • Not sure why this didn't cause an issue when we first updated to Fastify v4 (#46 )
  • Updated validate workflow to run tests on Node v14 as well as v16
  • Updated tap to latest version

Test plan

• Confirm validate workflow passes