fix(scm/webhook): turn off pr:edited events

[ecrupper]

Until we give users the ability to opt-in for the edited action for PR events, the added webhook noise is resulting in unexpected behavior.

For example, if a user has a step:

- name: example
   image: alpine
   ruleset:
      event: pull_request

That step is ignored due to the fact that pull_request == pull_request:opened, pull_request:synchronize. Another way to say this: we accommodated legacy pull request ruleset on the yaml side but not the webhook side.

As a band-aid, we can turn off the firehose for edited actions until we have a more robust way of handling it.

[codecov]

Codecov Report

Merging #677 (c3d7e9e) into master (9b27b07) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #677      +/-   ##
==========================================
- Coverage   54.96%   54.96%   -0.01%     
==========================================
  Files         195      195              
  Lines       15956    15955       -1     
==========================================
- Hits         8771     8770       -1     
  Misses       6811     6811              
  Partials      374      374              

Impacted Files	Coverage Δ
scm/github/webhook.go	86.06% <100.00%> (-0.04%)	⬇️