misc,python: Add pyupgrade hook to pre-commit

This hook automatically upgrades the syntax to recommended standards for
new versions of the language.

These are numerous and are outlined here:
https://github.com/asottile/pyupgrade

Change-Id: I73fc58a08160ed9a21cfa3b3e023c259a84592ba

.pre-commit-config.yaml

@@ -72,6 +72,13 @@ repos:
       rev: 23.9.1
       hooks:
           - id: black
+    - repo: https://github.com/asottile/pyupgrade
+      rev: v3.14.0
+      hooks:
+          - id: pyupgrade
+            # Python 3.8 is the earliest version supported.
+            # We therefore conform to the standards compatible with 3.8+.
+            args: [--py38-plus]
     - repo: local
       hooks:
           - id: gem5-style-checker