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Remove thread-unsafe Dir.chdir from Satellite#lock

This is made possible by changes in gitlab-grit 2.6.10.
Merge branch 'satellite_chdir' into 'master'

Remove thread-unsafe Dir.chdir from Satellite#lock

See merge request !968
Merge branch 'branches_with_no_parent' into 'master'

Branches with no parent cannot be merged

Solves `undefined method 'reduce' for false:FalseClass`

Fixes #1415

See merge request !967