build(deps): bump idna in /tests/opentelemetry-docker-tests/tests

Bumps [idna](https://github.com/kjd/idna) from 3.7 to 3.15.
- [Release notes](https://github.com/kjd/idna/releases)
- [Changelog](https://github.com/kjd/idna/blob/master/HISTORY.md)
- [Commits](kjd/idna@v3.7...v3.15)

---
updated-dependencies:
- dependency-name: idna
  dependency-version: '3.15'
  dependency-type: direct:production
...

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

Author: dependabot[bot]

tests/opentelemetry-docker-tests/tests/test-requirements.txt

@@ -21,7 +21,7 @@ flaky==3.7.0
 flask==3.1.3
 greenlet==3.0.3
 grpcio==1.63.2
-idna==3.7
+idna==3.15
 iniconfig==2.0.0
 kombu==5.3.5
 mysql-connector-python==8.3.0