Fix bug when redefining default workflow

[lkysow]

Previously, given the config:

  workflows:
    default:
      ...

We wouldn't actually use the redefined default workfow in our always
existing first repo config. This would mean that the redefined default
was never used unless users explicitly set workflow: default in the
repos array.

Fixes #860

[codecov]

Codecov Report

Merging #862 into master will decrease coverage by 0.04%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #862      +/-   ##
==========================================
- Coverage   71.83%   71.79%   -0.05%     
==========================================
  Files          65       65              
  Lines        5213     5216       +3     
==========================================
  Hits         3745     3745              
- Misses       1183     1186       +3     
  Partials      285      285

Impacted Files	Coverage Δ
server/events/yaml/raw/global_cfg.go	0% <0%> (ø)	⬆️

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