gitlab: 13.5.1 -> 13.6.0

Changed ruby version to 2.7.x to match upstream.
Added a gem config for gitlab-pg_query as it tries to download a source
tarball during the build process.
Also removed a patch for gitaly that has become obsolete by upstream fix
[here](https://gitlab.com/gitlab-org/gitaly/-/commit/de04077c25cc23b001317d2efdf5a9ead0bc86b9).

pkgs/applications/version-management/gitlab/gitaly/Gemfile

@@ -1,8 +1,5 @@
 source 'https://rubygems.org'
 
-# Require bundler >= 1.16.5 to avoid this bug: https://github.com/bundler/bundler/issues/6537
-gem 'bundler', '>= 1.17.3'
-
 gem 'rugged', '~> 0.28'
 gem 'github-linguist', '~> 7.11', require: 'linguist'
 gem 'gitlab-markup', '~> 1.7.1'
@@ -16,7 +13,7 @@ gem 'faraday', '~> 1.0'
 gem 'rbtrace', require: false
 
 # Labkit provides observability functionality
-gem 'gitlab-labkit', '~> 0.12.0'
+gem 'gitlab-labkit', '~> 0.13.2'
 
 # Detects the open source license the repository includes
 # This version needs to be in sync with GitLab CE/EE
@@ -33,10 +30,4 @@ group :development, :test do
   gem 'pry', '~> 0.12.2', require: false
 
   gem 'grpc-tools', '= 1.30.2'
-
-  # gitlab-shell spec gems
-  gem 'listen', '~> 0.5.0'
-  gem 'simplecov', '~> 0.17.1', require: false
-  gem 'vcr', '~> 4.0.0'
-  gem 'webmock', '~> 3.4.0'
 end