chore: update backend coverage target

[amandavialva01]

Description

Backend code coverage has increased to about 43%, so increasing the target to 42% (with the same 3% threshold).

Test Plan

CI passes.

Checklist

• Changes have been manually QA'd
• User-facing API changes need the "User-facing API Change" label.
• Release notes should be added as a separate file under docs/release-notes/.
  See Release Note for details.
• Licenses should be included for new code which was copied and/or modified from any external code.

[netlify]

✅ Deploy Preview for determined-ui canceled.

Name	Link
🔨 Latest commit	f89188e
🔍 Latest deploy log	https://app.netlify.com/sites/determined-ui/deploys/65c110dc3c1663000725082f

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (65c811c) 47.72% compared to head (f89188e) 47.72%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8798      +/-   ##
==========================================
- Coverage   47.72%   47.72%   -0.01%     
==========================================
  Files        1049     1049              
  Lines      167258   167258              
  Branches     2243     2243              
==========================================
- Hits        79824    79816       -8     
- Misses      87276    87284       +8     
  Partials      158      158              

Flag	Coverage Δ
backend	43.23% <ø> (-0.03%)	⬇️
harness	64.32% <ø> (ø)
web	42.53% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

see 3 files with indirect coverage changes

[dannysauer]

LGTM, after a week of study. :D