Add missing attribute job_runs in WorkflowRunBill

[marcelocarlos]

What type of PR is this?

Update WorkflowRunBill to include a missing attribute

What this PR does / why we need it

Brings the implementation inline with the expected API response (docs here).

WorkflowRunBill current implementation is missing the JobRuns (job_runs) attribute. This is important when calculating the actual cost and time spent in a given workflow run as the total_ms doesn't include the rounding ups or multipliers that GitHub applied to each job run.

[codecov]

Codecov Report

Merging #2206 (b046070) into master (a4ce810) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2206   +/-   ##
=======================================
  Coverage   97.79%   97.79%           
=======================================
  Files         112      112           
  Lines       10036    10036           
=======================================
  Hits         9815     9815           
  Misses        154      154           
  Partials       67       67           

Impacted Files	Coverage Δ
github/actions_workflow_runs.go	100.00% <ø> (ø)

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[gmlewis]

Thank you, @marcelocarlos !
LGTM.
Merging.