fix(status): set correct status after checkin

[wass3r]

closes go-vela/community#1016

since check-in can (and does) happen while processing builds, status is getting set to the wrong value. the fix uses the helper function to determine the proper status.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 6 lines in your changes missing coverage. Please review.

Project coverage is 62.02%. Comparing base (3db6801) to head (9ab5ad7).

Files with missing lines	Patch %	Lines
cmd/vela-worker/register.go	0.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #611      +/-   ##
==========================================
- Coverage   62.07%   62.02%   -0.05%     
==========================================
  Files         121      121              
  Lines        8166     8172       +6     
==========================================
  Hits         5069     5069              
- Misses       2871     2877       +6     
  Partials      226      226              

Files with missing lines	Coverage Δ
cmd/vela-worker/register.go	0.00% <0.00%> (ø)