Log Message:
libfolks: update to 0.15.5.

Unstable version, but stable branch doesn't build against
current vala package.

Overview of changes from libfolks 0.15.4 to libfolks 0.15.5
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Bugs fixed:
  * vapi: Add missing generic type argument

Overview of changes from libfolks 0.15.3 to libfolks 0.15.4
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Bugs fixed:
  * Fix docs build against newer eds version
  * Fix build against newer eds version
  * Remove volatile keyword from tests

Overview of changes from libfolks 0.15.2 to libfolks 0.15.3
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Bugs fixed:
  * Fix build against newer eds version

Overview of changes from libfolks 0.15.1 to libfolks 0.15.2
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Bugs fixed:
  * Fixed build errors after API version bump
  * Fixed gtk-doc errors due to missing version entities

Overview of changes from libfolks 0.14.0 to libfolks 0.15.1
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Dependencies:
  * No more dependencies on libtracker
  * GLib minimal requirement: 0.58
  * E-D-S minimal requirement: 3.38

Major changes:
  * This release drops the Tracker backend (along with its dependencies).
  * A selection of (small) performance improvements
  * Auto-generation and deployment of the docs using CI