Only ask integration_proxies for review for operator updates on main branch

[PProfizi]

While running test operator update actions, the integration_proxies keep being added as reviewer despite the generated PR being on a feature branch.
This limits it to operator update PRs on the default branch.

See here for example of if/else in GitHub actions expressions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.52%. Comparing base (50d0208) to head (13178b3).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2068      +/-   ##
==========================================
+ Coverage   86.40%   86.52%   +0.11%     
==========================================
  Files          90       90              
  Lines       10233    10233              
==========================================
+ Hits         8842     8854      +12     
+ Misses       1391     1379      -12