ci: Add absolufy-imports pre-commit hook (#1635)

* Add absolufy-imports pre-commit hook to ensure that absolute imports are used
   - Motivation comes from switching over to absolute imports in PR #1539
   - c.f. https://github.com/MarcoGorelli/absolufy-imports

.pre-commit-config.yaml

@@ -31,6 +31,11 @@ repos:
     - id: pyupgrade
       args: ["--py37-plus"]
 
+-   repo: https://github.com/MarcoGorelli/absolufy-imports
+    rev: v0.3.0
+    hooks:
+    - id: absolufy-imports
+
 -   repo: https://github.com/psf/black
     rev: 21.9b0
     hooks: