Apps-Service: Add baptiste-preview to ListRepos and ListUserRepos

[andygrunwald]

The preview application/vnd.github.baptiste-preview+json ensures that the field "is_template": false is part of the repository response of the Apps Service.

[codecov]

Codecov Report

Merging #1860 (80485d5) into master (cceb4d4) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1860   +/-   ##
=======================================
  Coverage   97.64%   97.65%           
=======================================
  Files         105      105           
  Lines        6764     6770    +6     
=======================================
+ Hits         6605     6611    +6     
  Misses         86       86           
  Partials       73       73           

Impacted Files	Coverage Δ
github/apps_installation.go	92.30% <100.00%> (+1.00%)	⬆️

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[gmlewis]

Thank you, @andygrunwald !
LGTM.

Awaiting second LGTM before merging.

[wesleimp]

💙

[gmlewis]

Thank you, @wesleimp !
Merging.