Merge branch 'release-3.9'. Close Copilot-Language#320.

**Description**

Version 3.9 of Copilot is ready and should be closed and published on Hackage.

**Type**

- Management: release and publication.

**Additional context**

None.

**Requester**

- Ivan Perez.

**Method to check presence of bug**

Not applicable (not a bug).

**Expected result**

- Cabal files indicate new version number, constraints are adjusted as
  needed, commit is tagged with version number, and packages are
published on hackage.

**Solution implemented**

- Cabal files indicate new version number, constraints are adjusted as
  needed, commit is tagged with version number, and packages are
published on hackage.

**Further notes**

- New version published on hackage.

Merge branch 'release-3.8'. Close Copilot-Language#298.

Merge branch 'release-3.7'. Close Copilot-Language#287.

3.6

Merge branch 'release-3.5'. Close Copilot-Language#247.

Version 3.4

3.3

Version 3.2.1

Version 3.2

Version 3.1