Update 'envconfig' to fix environment variables reads

[joanlopez]

What?

It updates the envconfig dependency to include a recent fix to adequately support nil marshalable pointers,
which is causing #3638.

Why?

After having discarded #3660, we decided (see here and here) to just push the fix to our own fork of envconfig, for simplicity.

Checklist

• I have performed a self-review of my code.
• I have added tests for my changes.
• I have run linter locally (make lint) and all checks pass.
• I have run tests locally (make tests) and all tests pass.
• I have commented on my code, particularly in hard-to-understand areas.

Related PR(s)/Issue(s)

Closes #3638

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.60%. Comparing base (2af1a3f) to head (7258fc2).

❗ Current head 7258fc2 differs from pull request most recent head d182d5d. Consider uploading reports for the commit d182d5d to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3672   +/-   ##
=======================================
  Coverage   73.60%   73.60%           
=======================================
  Files         277      277           
  Lines       20251    20251           
=======================================
  Hits        14906    14906           
- Misses       4399     4400    +1     
+ Partials      946      945    -1     

Flag	Coverage Δ
ubuntu	73.54% <ø> (+0.01%)	⬆️
windows	73.45% <ø> (ø)

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

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.