fix Dependabot integration

[carlosthe19916]

it seems that default_reviewers is needed since with this change it seems to work in my fork: https://github.com/carlosthe19916/xavier-ui/pulls

[codecov-commenter]

Codecov Report

Merging #105 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #105   +/-   ##
=======================================
  Coverage   71.47%   71.47%           
=======================================
  Files          62       62           
  Lines        1469     1469           
  Branches      285      285           
=======================================
  Hits         1050     1050           
  Misses        380      380           
  Partials       39       39           

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