chore: add pyupgrade pre-commit hook

Part-of: <https://dev.funkwhale.audio/funkwhale/funkwhale/-/merge_requests/2189>

.pre-commit-config.yaml

@@ -24,6 +24,13 @@ repos:
       - id: mixed-line-ending
       - id: trailing-whitespace
 
+  - repo: https://github.com/asottile/pyupgrade
+    rev: v3.2.2
+    hooks:
+      - id: pyupgrade
+        args: [--py37-plus]
+        exclude: ^(api/.*/migrations/.*)
+
   - repo: https://github.com/psf/black
     rev: 22.10.0
     hooks: