Minor: Fix confusing test description

[ivoanjo]

Leftover from #1560, I noticed that I had left a confusing description for a test group.

[codecov-commenter]

Codecov Report

Merging #1562 (d939bd9) into master (bd7eee4) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1562      +/-   ##
==========================================
- Coverage   98.24%   98.23%   -0.01%     
==========================================
  Files         885      885              
  Lines       42592    42592              
==========================================
- Hits        41843    41842       -1     
- Misses        749      750       +1     

Impacted Files	Coverage Δ
spec/ddtrace/metrics_spec.rb	99.61% <100.00%> (ø)
spec/ddtrace/profiling/ext/forking_spec.rb	99.38% <0.00%> (-0.62%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update bd7eee4...d939bd9. Read the comment docs.