chore(deps-dev): Update pyupgrade requirement from 3.20.0 to 3.21.0

Updates the requirements on [pyupgrade](https://github.com/asottile/pyupgrade) to permit the latest version.
- [Commits](asottile/pyupgrade@v3.20.0...v3.21.0)

---
updated-dependencies:
- dependency-name: pyupgrade
  dependency-version: 3.21.0
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

pyproject.toml

@@ -94,7 +94,7 @@ mypy = "1.18.2"
 bandit = "1.8.6"
 tomli = { version = "^2.0.1", python = "<3.11" }
 tox = "4.30.3"
-pyupgrade = "3.20.0"
+pyupgrade = "3.21.0"
 deptry = "0.23.1"
 # for tests, use the GPL-version of jsonschema format validators - they are faster
 jsonschema = { version = "*", extras = ["format"] }