fix: Remove custom Accept in Apps.ListRepos and Apps.ListUserRepos

[alexandear]

The PR removes no longer needed preview "Accept" headers in AppsService.ListRepos and AppsService.ListUserRepos.

https://docs.github.com/en/rest/apps/installations?apiVersion=2022-11-28#list-repositories-accessible-to-the-app-installation--parameters
https://docs.github.com/en/rest/apps/installations?apiVersion=2022-11-28#list-app-installations-accessible-to-the-user-access-token--parameters

[gmlewis]

Thank you, @alexandear!
Quick question - can any of these Preview constants be removed yet?

LGTM.
Merging.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.33%. Comparing base (2e26546) to head (80801cc).

Additional details and impacted files

@@ Coverage Diff @@## master #3609 +/- ##
==========================================
- Coverage 91.34% 91.33% -0.01% 
==========================================
Files 184 184 Lines 16180 16166 -14 ==========================================
- Hits 14779 14765 -14 
Misses 1227 1227 Partials 174 174 

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[alexandear]

Quick question - can any of these Preview constants be removed yet?

Nope, these constants still used:

❯ grep -r --include='*.go' --exclude='*_test.go' 'mediaTypeTopicsPreview' .
./github/repos_forks.go: req.Header.Set("Accept", mediaTypeTopicsPreview)
./github/teams.go: req.Header.Set("Accept", mediaTypeTopicsPreview)
./github/teams.go: req.Header.Set("Accept", mediaTypeTopicsPreview)
./github/activity_star.go: acceptHeaders := []string{mediaTypeStarring, mediaTypeTopicsPreview}
./github/search.go: acceptHeaders = append(acceptHeaders, mediaTypeTopicsPreview)
./github/search.go: acceptHeaders = append(acceptHeaders, mediaTypeTopicsPreview)
./github/repos.go: acceptHeaders := []string{mediaTypeTopicsPreview, mediaTypeRepositoryVisibilityPreview}
./github/repos.go: mediaTypeTopicsPreview,
./github/repos.go: req.Header.Set("Accept", mediaTypeTopicsPreview)
./github/repos.go: req.Header.Set("Accept", mediaTypeTopicsPreview)
./github/github.go: mediaTypeTopicsPreview = "application/vnd.github.mercy-preview+json"
❯ grep -r --include='*.go' --exclude='*_test.go' 'mediaTypeRepositoryVisibilityPreview' .
./github/repos.go: acceptHeaders := []string{mediaTypeTopicsPreview, mediaTypeRepositoryVisibilityPreview}
./github/repos.go: acceptHeaders := []string{mediaTypeRepositoryTemplatePreview, mediaTypeRepositoryVisibilityPreview}
./github/repos.go: mediaTypeRepositoryVisibilityPreview,
./github/repos.go: acceptHeaders := []string{mediaTypeRepositoryTemplatePreview, mediaTypeRepositoryVisibilityPreview}
./github/github.go: mediaTypeRepositoryVisibilityPreview = "application/vnd.github.nebula-preview+json"
❯ grep -r --include='*.go' --exclude='*_test.go' 'mediaTypeRepositoryTemplatePreview' .
./github/repos.go: acceptHeaders := []string{mediaTypeRepositoryTemplatePreview, mediaTypeRepositoryVisibilityPreview}
./github/repos.go: req.Header.Set("Accept", mediaTypeRepositoryTemplatePreview)
./github/repos.go: mediaTypeRepositoryTemplatePreview,
./github/repos.go: acceptHeaders := []string{mediaTypeRepositoryTemplatePreview, mediaTypeRepositoryVisibilityPreview}
./github/github.go: mediaTypeRepositoryTemplatePreview = "application/vnd.github.baptiste-preview+json"