[DRE-maint] Bug#983346: Update gitlab to 13.7.7 (installation fails - need help)

[Pirate Praveen]

Package: gitlab
Severity: important
Control: tags -1 help

I'm trying to update gitlab to 13.7.7 (master-13.7 branch in salsa),

but installation fails with

Bundle complete! 212 Gemfile dependencies, 393 gems now installed.
Gems in the groups development and test were not installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.
gitlab_production database is not empty, skipping gitlab setup
fatal: not a git repository (or any of the parent directories): .git
fatal: not a git repository (or any of the parent directories): .git
Attention: used pure ruby version of MurmurHash3
rake aborted!
Feature::InvalidFeatureFlagError: Feature flag 
'api_kaminari_count_with_limit' is al
ready defined in 
'/usr/share/gitlab/config/feature_flags/ops/api_kaminari_count_with
_limit.yml'
/usr/share/gitlab/lib/feature/definition.rb:165:in `block in 
load_all_from_path!'
/usr/share/gitlab/lib/feature/definition.rb:161:in `each'
/usr/share/gitlab/lib/feature/definition.rb:161:in `load_all_from_path!'
/usr/share/gitlab/lib/feature/definition.rb:146:in `block in load_all!'
/usr/share/gitlab/lib/feature/definition.rb:145:in `each'
/usr/share/gitlab/lib/feature/definition.rb:145:in `each_with_object'
/usr/share/gitlab/lib/feature/definition.rb:145:in `load_all!'
/usr/share/gitlab/lib/feature/definition.rb:102:in `reload!'
/usr/share/gitlab/lib/feature.rb:141:in `register_definitions'
/usr/share/gitlab/config/initializers/0_inject_feature_flags.rb:5:in 
`<top (required
)>'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/de
pendencies.rb:318:in `load'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/de
pendencies.rb:318:in `block in load'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/de
pendencies.rb:291:in `load_dependency'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/de
pendencies.rb:318:in `load'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/engine.rb:666:in
 `block in load_config_initializer'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/no
tifications.rb:182:in `instrument'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/engine.rb:665:in
 `load_config_initializer'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/engine.rb:625:in
 `block (2 levels) in <class:Engine>'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/engine.rb:624:in
 `each'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/engine.rb:624:in
 `block in <class:Engine>'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/initializable.rb
:32:in `instance_exec'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/initializable.rb
:32:in `run'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/initializable.rb
:61:in `block in run_initializers'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/initializable.rb
:50:in `each'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/initializable.rb
:50:in `tsort_each_child'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/initializable.rb
:60:in `run_initializers'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/application.rb:3
63:in `initialize!'
/usr/share/gitlab/config/environment.rb:5:in `<top (required)>'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/de
pendencies.rb:324:in `require'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/de
pendencies.rb:324:in `block in require'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/de
pendencies.rb:291:in `load_dependency'
/usr/share/rubygems-integration/all/gems/activesupport-6.0.3.4/lib/active_support/de
pendencies.rb:324:in `require'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/application.rb:3
39:in `require_environment!'
/usr/share/rubygems-integration/all/gems/railties-6.0.3.4/lib/rails/application.rb:5
23:in `block in run_tasks_blocks'
/usr/share/rubygems-integration/all/gems/rake-13.0.1/exe/rake:27:in 
`<top (required)
 >'
Tasks: TOP => db:migrate => db:load_config => environment
(See full trace by running task with --trace)
dpkg: error processing package gitlab (--configure):
 installed gitlab package post-installation script subprocess returned 
error exit st
atus 1
Errors were encountered while processing:
 gitlab
E: Sub-process /usr/bin/dpkg returned an error code (1)

Usually such errors come from an obsolete initializer, but 
0_inject_feature_flags.rb mentioned in the log is still present in 
upstream version.

Help in fixing this error welcome.