fix!: Return RepositoryAttachment from GetRepositoriesForCodeSecurityConfiguration

[ericmort]

BREAKING CHANGE: GetRepositoriesForCodeSecurityConfiguration now returns RepositoryAttachment instead of Repository.

Adds type RepositoryAttachment for GetRepositoriesForCodeSecurityConfiguration

Fixes unmarshal error in GetRepositoriesForCodeSecurityConfiguration, as described in #3217.

(I submitted the PR under my corporate GitHub user, but I could not get a proper google/CLA so using my personal user.)

[gmlewis]

Thank you, @ericmort!
LGTM.

Please note that I still don't have write access to this repo, but figure I might as well attempt to catch up on my code reviews (which I usually allow the linter to process first... ah, well).

NOTES TO SELF:

• Add to the description:
  BREAKING CHANGE: GetRepositoriesForCodeSecurityConfiguration now returns RepositoryAttachment instead of Repository.
• Add Breaking API label
• Change PR title:
  fix!: Return RepositoryAttachment from GetRepositoriesForCodeSecurityConfiguration

[gmlewis]

Fixes: #3217.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.11%. Comparing base (9febb45) to head (ecee97a).
⚠️ Report is 8 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #3707 +/- ##
=======================================
Coverage 91.11% 91.11% =======================================
Files 187 187 Lines 16684 16686 +2 =======================================
+ Hits 15202 15204 +2 
Misses 1295 1295 Partials 187 187 

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[gmlewis]

@ericmort - would you mind resolving the conflicts in this PR or would you like me to do that?

[ericmort]

@gmlewis I resolved it now

[gmlewis]

@gmlewis I resolved it now

@ericmort - could you please investigate the lint and test failures?

[gmlewis]

Thank you, @ericmort!

cc: @stevehipwell

[stevehipwell]

LGTM

[gmlewis]

Thank you, @stevehipwell!
Merging.