Bump idna from 3.3 to 3.7 in /testapp

Bumps [idna](https://github.com/kjd/idna) from 3.3 to 3.7.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.rst)
- [Commits](kjd/idna@v3.3...v3.7)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

testapp/requirements.txt

@@ -3,7 +3,7 @@ attrs==21.4.0
 certifi==2023.7.22
 charset-normalizer==2.0.12
 jinja2
-idna==3.3
+idna==3.7
 iniconfig==2.0.0
 greenlet==2.0.1
 packaging==21.3