Repository.ListByOrg: Add nebula-preview to receive visibility field

[marcelocarlos]

What type of PR is this?

feature

What this PR does / why we need it:

In addition to the changes added in #1780, this change also ensures the Visibility field is included when calling Repositories.ListByOrg.

Special notes for your reviewer:

None

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[marcelocarlos]

@googlebot I signed it!

[codecov]

Codecov Report

Merging #1795 (22cb4f1) into master (24b281b) will not change coverage.
The diff coverage is 100.00%.

@@ Coverage Diff @@## master #1795 +/- ##
=======================================
Coverage 97.54% 97.54% =======================================
Files 98 98 Lines 6383 6383 =======================================
Hits 6226 6226 Misses 85 85 Partials 72 72 

Impacted Files	Coverage Δ
github/repos.go	98.70% <100.00%> (ø)

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[gmlewis]

Thank you, @marcelocarlos !
LGTM.
Merging.