fix: correct endpoints for custom roles

[joshua-hancox]

This function was created based on the docs here:
https://docs.github.com/en/rest/orgs/custom-roles#list-custom-repository-roles-in-an-organization

The docs incorrectly give the endpoint https://api.github.com/organizations/ORGANIZATION_ID/custom_roles.

When using this function, I get a 404.

The correct endpoint for the custom_roles endpoint is https://api.github.com/orgs/ORGANIZATION_ID/custom_roles - and this is consistent with other github endpoints under orgs. I have raised a support ticket with github, but I would expect them to change the documentation, not the api endpoint.

Also changed the file names for consistency.

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[joshua-hancox]

Hey both @gmlewis @tamboliasir1!

Could you take a look at this change for me when you get a second please?

[codecov]

Codecov Report

Merging #2370 (f08b039) into master (0cf45d2) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2370   +/-   ##
=======================================
  Coverage   98.06%   98.06%           
=======================================
  Files         119      119           
  Lines       10545    10545           
=======================================
  Hits        10341    10341           
  Misses        140      140           
  Partials       64       64           

Impacted Files	Coverage Δ
github/orgs_custom_roles.go	100.00% <100.00%> (ø)

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[gmlewis]

Thank you, @joshuahancox !
LGTM.
Merging.