Fix helm secret syntax in terraform example

[iamhsa]

What this PR does / why we need it: The code in the terraform example has a bad argument in the helm secret call. This PR corrects it.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #497

Special notes for your reviewer: I haven't modify the Changelog.md has it's just a small modification in an example.
Let me know if you think it's necessary.

PR Readiness Checklist:

Complete these before marking the PR as ready to review:

• I haven't modify the Changelog.md has it's just a small modification in an example.
  Let me know if you think it's necessary.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.41%. Comparing base (036be0e) to head (2a94aed).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #498   +/-   ##
=======================================
  Coverage   87.41%   87.41%           
=======================================
  Files          22       22           
  Lines         842      842           
=======================================
  Hits          736      736           
  Misses        106      106           

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[jkroepke]

Thanks!