Bump the python-packages group in /backend with 2 updates

Bumps the python-packages group in /backend with 2 updates: [coverage](https://github.com/nedbat/coveragepy) and [testcontainers[postgres]](https://github.com/testcontainers/testcontainers-python).


Updates `coverage` from 7.6.8 to 7.6.9
- [Release notes](https://github.com/nedbat/coveragepy/releases)
- [Changelog](https://github.com/nedbat/coveragepy/blob/master/CHANGES.rst)
- [Commits](nedbat/coveragepy@7.6.8...7.6.9)

Updates `testcontainers[postgres]` from 4.8.2 to 4.9.0
- [Release notes](https://github.com/testcontainers/testcontainers-python/releases)
- [Changelog](https://github.com/testcontainers/testcontainers-python/blob/main/CHANGELOG.md)
- [Commits](testcontainers/testcontainers-python@testcontainers-v4.8.2...testcontainers-v4.9.0)

---
updated-dependencies:
- dependency-name: coverage
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: python-packages
- dependency-name: testcontainers[postgres]
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: python-packages
...

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

backend/requirements.txt

@@ -1,4 +1,4 @@
-coverage==7.6.8
+coverage==7.6.9
 Twisted==24.11.0
 psycopg2-binary==2.9.10
 pylint==3.3.2

backend/tests/requirements.txt

@@ -1,5 +1,5 @@
 ddt==1.7.2
 psycopg==3.2.3
 pytest==8.3.4
-testcontainers[postgres]==4.8.2
+testcontainers[postgres]==4.9.0
 unittest-xml-reporting==3.2.0