ci: update nomad api weekly

[lukasmetzner]

Schedule github.com/hashicorp/nomad/api to be updated on every Sunday of the week. As github.com/hashicorp/nomad/api is not properly versioned we receive a new PR (or PR update) for every new git commit on the main branch of github.com/hashicorp/nomad/api.

github.com/hashicorp/nomad has no fixed release dates, so checking after every work week might be a suitable choice.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 32.38%. Comparing base (361f16e) to head (cc1a18f).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #854   +/-   ##
=======================================
  Coverage   32.38%   32.38%           
=======================================
  Files          21       21           
  Lines        2075     2075           
=======================================
  Hits          672      672           
  Misses       1369     1369           
  Partials       34       34           

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