Update flask requirement from <2.4,>=1.1.1 to >=1.1.1,<3.1 (#6390)

Updates the requirements on [flask](https://github.com/pallets/flask) to permit the latest version.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/main/CHANGES.rst)
- [Commits](https://github.com/pallets/flask/compare/1.1.1...3.0.0)

---
updated-dependencies:
- dependency-name: flask
  dependency-type: direct:production
...

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pyproject.toml

@@ -35,7 +35,7 @@ dependencies = [
     "Brotli>=1.0,<1.1",
     "certifi>=2019.9.11",  # no semver here - this should always be on the last release!
     "cryptography>=38.0,<41.1",
-    "flask>=1.1.1,<2.4",
+    "flask>=1.1.1,<3.1",
     "h11>=0.11,<0.15",
     "h2>=4.1,<5",
     "hyperframe>=6.0,<7",