chore(deps): update flake8 requirement in /compose/backend (#1153)

Updates the requirements on [flake8](https://github.com/pycqa/flake8) to permit the latest version.
- [Commits](PyCQA/flake8@3.8.0...7.3.0)

---
updated-dependencies:
- dependency-name: flake8
  dependency-version: 7.3.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

compose/backend/pyproject.toml

@@ -43,7 +43,7 @@ dependencies = [
 
 [project.optional-dependencies]
 dev = [
-    "flake8~=3.8",
+    "flake8~=7.3",
     "pip-chill~=1.0",
     "wheel~=0.36",
     "pytest~=8.4"