[3.13] Enable colour for doctest on GitHub Actions (GH-123536) (#123538)

Enable colour for doctest on GitHub Actions (GH-123536)
(cherry picked from commit 0cba289870)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>

.github/workflows/reusable-docs.yml

@@ -11,6 +11,9 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
   cancel-in-progress: true
 
+env:
+  FORCE_COLOR: 1
+
 jobs:
   build_doc:
     name: 'Docs'